In desperate need of help PLEASE SOMEONE ANSWER?!!!!!!!!!?

in school we have to build a boat that has tin foil on the outside of it and it can only have a skeleton in it so my teacher said he has to be able to poke through it what are some ideas to help make it float i had an idea Of putting Styrofoam at the bottom any ideas for what else i should put in it to help float? P.S whoever has the best boat get a 5% bonus PLEASE HELP ITS DUE ON THURSDAY APRIL 18 PLEASE HELP!?!?!?!?!?!?