I agree with items that are useful or have some sentimental value. Better to have 1 or 2 high quality items that the kids will love than a bag full of junk. I remember when I was competing I got a notepad from a local community college at a meet, what kid wants that?
Hair scrunchies, flowers, or ribbons are fun and somewhat easy. I think you get free scrunchies if you are doing GK leo sales at the meet. If you want to get more creative, lots of crafty parents are good at making flowers/ribbons- you might be able to get a group together and make a fun activity out of it. There are also lots of people on Etsy or just little local businesses that make those sorts of things and I'm sure they would give you a deal, I guess it would depend on where you are located and how big that kind of thing is. When I lived in Utah everyone and their dog made hair accessories! If you go on Etsy you can do a search for local vendors, you might be able to find someone that makes that type of thing in your community-
Etsy - Local
Grip bags/tote bags (either purchased or made by team parents), tape/pre-wrap, t-shirts, scorebooks, journals, soffee type shorts with meet name, water bottles, pens/pencils are all good. I once got a bear with a t-shirt with the gym name on it that I liked, maybe you could even get the meet name on it. Or items that tie into the meet theme. I went to a Chinese New Years themed meet once and we got a bear with Chinese characters on it, a bracelet with Chinese characters, etc. Places like Oriental Trading are good for those more general products.
Talk with team parents and see if any of them work for or have connections to a business that could help (t-shirt company, screen printing or graphic design company, candy/food production) or have skills they would be willing to put to use. Good luck and have fun with it!