Hi A.,
I have been "Team Mom" for so many team and sports I've lost count. My boys are now 20 and 22 and I was involved with their baseball, soccer, football, basketball and boyscouts since they were 4 and 5 years old.. The easiest end of season party is at a pizza place. Make the date that is close to if not after the last game. Do not try to please everyone or try to get the date/place that certian parents want. Just make to date, and they can be there or not. Trust me on this one.
I usually gave out goodie bags to each child and a small gift to each coach or parent that helped for the whole season. This could be a plaque, personalized t-shirt or something that fits the coach's likes or personality. One year we had this coach that kept the boys practicing until it was dark. So as a gag, we got him those headband flashlights. We got him something else as well.
Also as a Team Mom it is helpful if you make a schedule for parents to rotate snacks, orange slices at half time healthy snacks for after. Send a sigh up sheet around, then follow up. You will have to keep on top of parents, remind them of their turn for snack ect. or you will have a lot of hot, cranky kids. It is also helpful to send out a game schedule or who you are playing and when, where.
I'm from the west coast and we also made our own banners. I'm not sure how it is done here, but if you need any other advice here's my number. I kind of miss those crazy busy days of when my boys were in sports. Have fun.
C. ###-###-####.