1. Get one of these:
If you think you need more than this, you don't! Resist your consumer lifestyle urges to pay extra for a carry-on or a checked bag. You chose this airline for a reason! Stuff your backpack to its brim, and bring a clutch for phone, wallet, and boarding pass-type essentials. Or, if you're a menswear wearing person, make the most of your large pocketed jeans and shorts. Maybe throw in a chapstick, if you're going to Denver.
2. Pick two to three bottoms only.
There is some strange, unwritten observance that, whenever we travel, we imagine we'll suddenly start wearing all of the outfits that have been hanging in our closets at home for months. In normal life, do you wear the same pair of jeans many times in a row without washing them? Bring those jeans! Why do we think that when we travel we are going to become miraculously cleaner, fresher versions of ourselves? Unless you're rolling in mud or are a very sweaty sweating machine, you can wear something more than once. Your friends are used to seeing you in the same five outfits, mix 'em, match 'em, and save your space.
3. Choose your shoes.
The heaviest ones go on your feet. If it's summer, pack sandals. If you need sneakers, get some flat folding ones like these. Let your footwear be comfortable and your walks will be plentiful.
4. Have a Kindle.
Budget flying leaves not much room for books. Reading apps can fit hundreds of them. Choose your battles.
5. Only laptop if you really, REALLY need to.
You are escaping! Stop working! Save your computer activities for low-level days like Monday :( or Tuesday :/. A tiny personal item restriction is a great excuse to be freely traveling without your ties. If you really need it, your phone does many of the same things in a more portable way. If you're traveling a budget airline for a work trip, find a better job.
6. Unlimited underwear.
Have small underwear that can squeeze in any extra space. Remember what I said about sink-washed underwear before, and give yourself this simple luxury.
7. Respect the limits of Ziploc bags.
I don't know the point of toiletry bags other than making me look very put-together and grown up. Many of us are not those things on a regular day, so why choose now to pretend? You'll need the baggie for security, anyway, so fit your toiletries in one and call it a day.
7. Go somewhere cool.
So that you care more about what you're heading towards than what you're bringing with you. Try Colorado. They have a lot of good looking sights to see.
8. Bring some friends.
Maybe they'll share the stuff that you couldn't fit! Remember that all you really need is the unmatched license/passport, credit card, phone combination, and head on your way.
*Note: This process has served me well for 3 to 4, maybe 5-day trips if it's beach weather. If you are budget flying for longer, I respect you and await your tips for the packing.