Back when I was a team dad all of us team parents had a gym kit we carried around for our teams. We all customized for our athletes (mine was all-girl) but knew that we could help each other out if something was missing.
I'll put a list here and change it as I remember stuff:
Athletic tape
Motrin (ibuprofen)
Tylenol
Benadryl (for allergic reactions)
A "girl kit" (in a discrete portable pouch - don't show it, just hand it to them when they have to tend to young lady needs)
Bobby pins
Hair bands
Safety pins (saves emergency uniform splits)
Crazy glue (fixes bows and uniform sequenze and stuff)
Tide bleach stick
Your team's make-up kit
First aid kid
Waters
Energy/meal bars
Snacks like fruit and little snack packs
A pouch to store rings/necklaces/earrings during competition
Spare bows
Potable charger with multiple USB inputs and/or spare chargin tips
I'll edit and add as required. This may help with a goody bag idea, but you'll find if the kids know you have a kit like this they will start coming to you whenever they need something.