Had a lot of school trips but as far as overnight, I'd have to go with the 5th grade trip to the beach in Morehead City, NC.

For us, in 3/4/5th grade we had trips that were for 3days and 2 nights:
3rd - It was Betsy Jeff Penn
4th - Camp Thunderbird
5th - The Beach

3rd and 4th trips were cool (in hindsight - no way I would have let my kids take a trip away that long, that early but hey...being a kid in the 80s was different time, lol)

5th grade seemed like the ultimate:
- last year before heading to middle school
- Young enough to enjoy the kid stuff still (the food / enjoying the beach / seeing the counselor get bit by a blue crab, lol)
- starting to realize your powers (or lack thereof depending on where you fell at the time) with the ladies