like donut holes or cookies...
You could even make chocolate chip cookies now and freeze them.
What we have done before, is make cookies for everyone, then we lay some on a cookie tray and write HAPPY BIRTHDAY YOUR NAME HERE (one letter per cookie) on the cookies on the tray.
We then put one or two candles in several cookies (to get to the appropriate number).
It is really so much easier for the camp staff -- handing out a cookie or two to each kid...
I love some of these ideas...they are very appropriate considering your user name.

I don't HAVE to bring cake for all the campers, I volunteered to do it. (Although I will admit I did not expect 150 to be the number of people to serve!) These are all kids that my son has been spending alot of time with over the past 2 years--even the bigger tweens/teens will often help out in the younger kid's classes. Their Sesei (karate instructor) makes a big deal of every kid's birthday in front of the group. I love it--and it really makes each kid feel special. They have a special song and dance they do all led by the older karate students from the dojo.
Even though this is a sleep away camp it's only about 15 minutes from our house so it wouldn't be a prolem to keep the cake cool until serving time.
I was thinking cupcakes would definately expedite the serving process that's why I was considering those instead. Then there are no forks/plates/cutting of the pieces needed.
I'm going to call Costco now and see what they say about paying the upcharge.