College Graduation

It`s my first time planing and hosting a graduation party and I`m very clueless on what to do. My party is going to be out doors at a local park. I`m planing on having it in the end of June to mid July. The tempture can be anywhere from 70-90 degrees. I`m kinda worryed about the weather...and the food. How do I keep things cold? i know that I need ice, but the ice will melt right? what kind of decorations can I use? most likely my theme is going to be "Shooting for the stars" It`s the most easyest to think of concidering I can find a lot of things with stars. Do you know of any that is easer? how do I keep my guest entertanined with out spending too much money? are there any other web sites that will give me good paryplaning advice?? PLEASE HELP......