I make it easy on myself...I just print labels with a cute graphic saying have a great summer, I'll miss you, thanks for making this year special, etc. and stick them on the comment section. Saves a TON of time at a very busy time of year.
I like to find something that each child has shown improvement on during the year, and focus on that. Leaving a positive reflection on 2nd grade gives each child a hope of a great 3rd grade.