I would suggest that you start a swim club and find someone that has an indoor pool or look to rent one. Look to start a few in different communities so you can have swim meets.
Start a debating club in different neighborhoods or from different camps so you can hone your skills and then meet up for some real fun! Get the counselors involved as the judges.
Start a book club where you can read books and get together Motzei Shabbos to discuss them and make recommendation lists for your schools, book stores and/or libraries either by age or by topic.
Start an exercise, dance or talent group. Whether it is art, music, singing, drawing, sewing, knitting, creative writing, computers etc. You can ask one of the parents or different parents to teach the group and you can help each other get better and one thing or another.