NBR: Food for an outdoor 30th birthday party (kinda long)

SoonToBeMsP

My DH is turning 30 next month and I am throwing him a huge outdoor party. He's a little bummed about the big 3-0 and I wanted to celebrate him before our LO came along. I've already got the entertainment (moon bounce type thing, rock wall, etc) but am stuck on the foods.

Ideally I'd like to make the food to save some money, but there is the possibility of ~60 people showing up (still waiting for RSVPs). And there is also the issue that this is a surprise. Yeah. Thankfully my mom lives nearby, so I could go over to her house to "hang out" and prepare some dishes... But what to prepare?

What would be good for:

-cooler weather (probably high 60s)

-easy to eat

-doesn't require reheating

-can be made a couple days in advance 

We don't have an electrical outlet at the site but there is a grill.

Ideas I've had include hamburgers/cheeseburgers, hot dogs, potato salad and chicken salad. I've also thought about two crockpots of chili, and hoping that they stay hot long enough...

Help please!