How to pack only in a Spirit Airlines free carry-on bag

Ultra low-cost airline carriers, such as Spirit Airlines, hook you in with really cheap fares -- like $19 one-way flights. It's not a scam, you really can fly miles above the earth's surface from around just $19 each way per person (or perhaps even cheaper with a kids fly free deal tacked on if you're flying Frontier).

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But, as you likely know, the total price to fly can also easily go up dramatically from there with ancillary fees. One way the true total cost to fly can jump up quickly is if you start paying for checked or carry-on bags. The fees to bring your own full-sized carry-on bag on the plane vary, but if you are listing your bag(s) during the initial trip booking, expect to pay about $30 for each checked bag and $35 for one carry-on bag both ways. If bags are overweight or oversized, they will incur additional charges from $30-$150.

But -- you don't have to pay those fees. If you can pack just the essentials using a backpack or similar, you can enjoy the heck out of your inexpensive airline ticket and leave the fee-paying to other passengers.

Related: Everything you should know before flying Spirit Airlines

Now to be fair, I love stuffing my Rimowa carry-on and personal-sized purse or backpack to the brim when bags are included in my airline ticket. However, I've also learned to forgo my regular full-sized carry-on in favor of a free Spirit Airlines-approved carry-on when necessary.

When you fly Spirit Airlines, you can bring on a personal item up to 18 x 14 x 8 inches on board for free while a full-sized carry-on will cost you $35 and up, depending on when and where you purchase the right to bring the bag on board. (Prices slightly less for $9 Fare Club members.)

If it’s just me for a short trip and I’m flying Spirit Airlines, I’m not paying for a bag if I can help it. Instead, I’m going to pack for a Spirit Airlines free personal carry-on. Here's how.

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Choose the right bag

First things first, you need the right bag to avoid Spirit Airlines bag fees. I have used my much-loved Sole Society Tote with regularity, but a regular backpack can work, too, as long as it is within the set parameters.

I’ve found that small traditional backpacks, such as the one an average middle schooler might take to school, are pretty good about staying within those size guidelines. Many of the fancier and larger backpacks are technically too large. However, Spirit Airlines doesn’t have a reputation for being overly strict with requiring passengers to stay exactly within the size guidelines.

Wearing my trusty Samsonite Modern Utility Double Shot Backpack (sized at 12" x 8" x 18" with a laptop compartment) has worked wonders when avoiding carry-on bag fees. I've even been known to use a Mickey backpack from time to time -- which works especially great if you are heading on a quick trip to Disney World.

Related: Just how small is the free Spirit Airlines carry-on

Going over the stated measurements an inch here or there with a bag you are wearing or carrying probably won't be a big deal with Spirit. However, straying too far from the stated maximum sizes for a free personal carry-on item may cost you, so we don't recommend that approach. If you aren't sure where to start, here's a look at some of our favorite carry-on backpacks.

Essentials only

Now that you have your Spirit Airlines-approved personal carry-on bag identified, you get to stuff it full with your absolute essentials. And I mean, the absolute essentials.

Related: 14 packing hacks for traveling with just a carry-on

For me, this often means a laptop, wallet, a tightly rolled change of clothes and then several smaller bags that will each hold specific items. I have one bag for my computer cords, one for my smaller clothing items like pajama shorts, underwear, etc., a bag for make-up and a final bag for toiletries.

I don’t want any of those items loose in my small personal carry-on item, nor do I want them mingling with each other. If you don't need special toiletries or make-up, then you'll have more space for clothes than I usually do.

Related: Everything you should know before flying Spirit Airlines

When you are packing for a free Spirit Airlines personal carry-on, you probably are only going to bring one pair of shoes -- the ones on your feet. Occasionally I can also sneak a pair of extra flats into my bag, but that's about it. You'll also want to carry your coat on board, if needed, even if it's warm where you're starting from.

Diaper bags fly free

It's OK to skimp on how many shoes or hair products you travel with, but you don't want to skimp on supplies for your young kids. Fortunately, an infant diaper bag can also come aboard for free -- assuming you are flying with a baby.

You never want to run out of formula, kid-friendly snacks, diapers, wipes and a change of clothes for a little one on a flight. Kiddos can also bring a car seat and stroller along for free.

Related: How to open frequent flyer accounts for your kids with the major U.S. airlines

Consider paying for one bag for the family

Only you know your budget but if you are flying Spirit without little kids for a short weekend trip, it can be realistic to avoid Spirit bag fees and pack everything in a free Spirit carry-on -- especially if you're going somewhere warm. If you're flying with little kids or are heading on a longer trip, I think it's worth it to pay to check or carry-on at least one bag for the family.

Everyone can still have their free personal item, but then pack additional items in the shared larger bag that you pay to bring. Just book the bag in advance online to pay the lowest rate. If you have a credit card with an annual travel credit, this could be a good way to use some of that credit. In fact, I'm switching my Amex airline fee credit selection to an ultra low-cost carrier for this very reason.

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Overall recommendations

The one downside to be aware of when loading up a free Spirit personal item to the max is that it might get really heavy. I was able to bring most everything I would have brought along if I packed in my regular roller carry-on on a recent two-night trip, but the difference was I was carrying all of that weight on my arm instead of rolling it behind me.

I would guess my bag ended up weighing close to 20 pounds, and after a while of carrying that on your arm, it starts to get uncomfortable. It would have been easier if I had gone the backpack route on that trip, rather than the tote.

Just be sure and factor in the weight you will be carrying to the equation, especially if you have any physical limitations, are managing young children or simply have to walk a very long distance before you get somewhere where you can unpack.

In many cases you don't need to pay to bring bags on board a Spirit Airlines flight, you just need to know how to pack for the free Spirit Airlines carry-on bag.

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With additional reporting by Mimi Wright.