How can I throw a surprise party for my boyfriend?

My boyfriends 30th birthday's coming up in April and I want to throw him a surprise birthday party but I'm horrible at planning stuff and bad at keeping things from him. Any sugggestions of what to do? I'm inviting his navy friends that he hasnt seen in almost 4 years, but I dont know where to have the party, what to buy (food/drinks), what to do (activities)... help please!

JWharton,
Let's first start off with the basics...
Budget.. Please know that if you have the money and don't spend it right he'll think you're cheap... So spend what you can.;-)
Anyway, the planning isn't as hard as you think. Here's a few steps to follow for this party:
* Get suggestions from his Navy friends (as a veteran myself - no one knows me like my old 'salty dog' friends)
* you know what he likes to eat.. Have that!! (If you're not great in the kitchen... Have it catered..but don't forget the budget thing)
* You can't go wrong with theming the event out... Whatever he may be into... Use that as a starting point on the theme.. Example: He likes golf.. Arrange for him and his 'buds' to have a round of golf at the local links. (Once again.. Don't forget your budget)
* Every idea you come across... WRITE IT DOWN!!! ( A short pencil is good for a long memory.
I know this was long but I hope it can be useful....
Good luck

Perfect I wanna give someone an idea for a party. Buy like chips food cake and stuff like that. and now have a Hawiian themed party with tikis and limbo!!