How to have an awesome pool party/sleepover with a budget?

By budget I mean were not going to buy like ANYTHING except food. There will be 4 girls (including me) all 11 (or almost 11) and usually when I have 1 on 1 sleepovers the girl always picks up the computer and types in "what to do at a sleepover when your bored" and my heart sinks! Like we can be having a totally awesome time and then THAT always happens! So 3 girls (maybe 2) are coming to my grandpa's pool. He has floating devices and a diving bored with water going up to 8 ft. and lounge chairs, and it'll be at night and he has a light in the water that makes the water change color, but I'm scared that won't "be enough" for my friends! Were having burgers and hotdogs, then go home at 10 and have an icecream sundae bar (probably just vanilla icecream with chocolate sauce and maybe m&m's). Also, at like every birthday party or whatever they are always having that "look" on their faces like "this is so lame." We feel like we go crazy and buy a bunch of stuff but thats never good enough for them! How can we have an awesome time??My mom isn't strict, but she doesn't want us ding-dong-ditching someones house or whatever. We have nail polish, but I'm sure everyones nails are already painted. We don't own any good movies. Sorry I'm probably tying your hands pretty well. PLEASE HELP!