Do a raffle for a pair of tickets to a football game in the next town. It helps if the home team is the Patriots.
We should make some good scratch with that. (You wanna buy a raffle ticket? Only $20 for a chance at some good seats. Should I put you down for two? Going quick -- you only got until Saturday!)
Not very good now but do a can/bottle drive (if you have 5c returnables). We do one in the fall and spring, after thanksgiving and graduations. (After New Years is another good one; outside the school on Kickoff Morning!) With plenty of advance notice (local newspaper, school flyers -- make sure the people that have cans know about it!) and cooperation with a bottle recycler, people will drop off tons of cans.
Another "easy" one: we go to our local Stop and Shop grocery store and ask for money from the customers. We bring last year's robot and have bright and smiley students ask. To tell the truth I don't think of it for the money (though we do good), but for getting the team in the town's eyes, having students being able to talk robots with interested adults, and occasionally get a mentor or sponsor. (We got a major sponsor this way; a town resident liked the lights on the robot and talked to his company to help sponsor us.)
The main thing about these is getting the students to realize the little work now saves the team money for travel, hotels, and yes, robot parts that somebody has to pay for.