I've had two jobs, didn't get my first one until almost 19 (which I am now) so from that I say the sooner you start the better.
DO NOT go for a cashier job, it will be the worst time ever. The problem is, there aren't a lot of other options for someone under 18. I can think of plenty entry-level alternatives to cashier, all requiring at least 18 years of age. But maybe you can be the person at a grocery store who stocks shelves or does the carts. If you're applying to a grocery store though they might try to give you a cashier job anyway but just say no thanks. I would not recommend it. That's my most important piece of advice.
When you turn 18, if you look for another job.. look on craigslist for a start it actually really helped me even though I never ended up applying to those jobs I listed down. But don't limit yourself to just that, a small majority of people advertise jobs there. Look in the newspaper (mostly degree-seeking employers but sometimes entry-level), and finally just randomly apply to places even if you think they're not hiring. That's how I got my current job.
I work at a day care with kids, I thought it would be terrible for me, but I can openly talk to kids a lot better than I can talk to adults, so it's actually a pretty good first job for me. Just try to find something you feel you'd be most comfortable doing, don't try to go for any job out there, unless you have to.. Try and find something you feel you would be ok doing, I know thats hard to do, because I had no idea I'd be good with kids, but I guess you just have to take a chance, and if the job isn't for you then you could always look for another where you'd feel more comfortable.
My first job was at a Subway when I was 16. It was okay. I did some cashiering, mostly prepping food. It was actually not a bad first job at all. what I had a problem with was my coworkers. I don't know if its bc I am serious or what, but I didn't fit in with them. I left bc I moved for college. My second and third jobs were in retail clothing stores. AVOID!! lol. A lot of folding, like hella folding until your wrists hurt. Dealing with people was bad only bc of my SA. It's only annoying bc you have to pick up clothes all day.
Current job is at a school!! love it!!
My advice, apply everywhere! You might not get your first choice, unless you're lucky. Try to avoid food jobs, but if that's all you get it's not a bad place to start. You might not get trash duty but you will probably get cashiering jobs. They're actually fun. You get out of the house. best of wishes
Most of the jobs I have received were me doing something alone, so I can't tell you much.
Like another poster here, I also had experience with kids. I used to be a "teacher" to groups of elementary school kids, and frankly, I loved it. I deal with children better than adults, so it made the job a lot easier.
Even if its retail or cashier, I bet they'll be good experience in overcoming SA.
Hm...the only real seasonal job I had was at a Firework store, but I don't think most states can legally have those. I worked mainly as a cashier. It was kind of horrifying at first, but it didn't take me long to learn generic phrases to handle most situations.
Though my first job was cleaning rooms at a motel. It was actually pretty easy as you don't have to deal with customers very often, except when straightening rooms. But I'm not sure that's an easy job to get.
I also dishwashed at the restaurant of the same place. That was an awful job, but not for social reasons. I think it might be a lot easier to get hired at such a job, since we always had people quitting.