Lots of people do this. In Europe it's a tradition going back hundreds of years, so it's not silly at all to plan for it! Don't feel like you need to be some kind of rebel punk outcast just to qualify as a legitimate traveler. Those guys do exist and for some of them the traveling life is a method of survival, but my sense is that the majority of people on the road are seasonal, part-time or gap year/sabbatical travelers. (Though they might not always recognize or admit it themselves.)
One of the important things about traveling is that while you can prepare for the unexpected, almost always you're gonna find yourself in a situation that you didn't prepare for and find yourself wishing you had some gadget or item that you could've brought but didn't, while at the same time you're hauling a bunch of shit you thought would be useful but actually wasn't. So the main piece of preparation you can do is mental, being able to cope with plans changing, with being temporarily uncomfortable because you took a wrong turn or made a wrong choice, and with having the resilience and common sense to not freak out and get yourself back on track.
Lots of basic life skills that you use on the road are applicable to regular housed up life too, especially if you are living alone and/or on a strict budget.
Learn to keep your body clean and lean. Learn to feed yourself with affordable, simple and healthy meals. Learn to tidy up after yourself. Think about how you'd do all those things if you had to carry all the stuff you used in a day on your back, and if you had no refrigerator or access hot water. Imagine in some places not even having access to cold water, and how much more shitty it'd be to have to carry all the water you're gonna use for everything on your back. Getting into long distance hikes or camping as a hobby is something that can give you these experiences outside of long term travel.
Learn how to blend in and avoid pissing people off. That doesn't mean being conformist, it just means not being offensively present. Easier for some people than others due to immutable physical characteristics, but there's ways to remain "invisible" even when you stick out, and it's a good skill to have. Big part of it is confidently just doing your thing and not exuding anxiety, which is tough when you're in a new or foreign place, but it'll pay off.
If you want to spange, it's worth learning some kind of performing art because that's exactly what spanging is. Whether a bit of comedy or storytelling or play an instrument or juggle or how to put on a sympathetic face that makes people want to give to you. If you don't want to spange, get some reps in doing after school work so you can prove to employers on the road you are reliable and know how to look professional, follow instructions and get shit done.
Most of all stay focused on having fun. Gap year or Grand Tour/OE etc shouldn't feel like an obligation, it's where you get to spread your wings and figure out the world how it is away from the places and people you knew growing up. If you have the privilege to quit when the going gets tough, no shame in doing that. Doesn't take away from the things you'll learn and the fun you'll have. It's not supposed to be a trial by fire, no gatekeeping required, it's your life, you get to choose what you want from travel and how best to do it your way.
