What are some 5th grade math activities?

Since you're going to be in a library how about doing elapsed time for a reading activity or how long different activities take. Say : Sally began reading at 11:25 AM. She read 4 books until 1:45 PM. How long did Sally read? For area and perimeter you can have them measure a mountain of things, for example, books, file cabinets, book shelves, etc. Use your imagination. Kids at that age love hands on stuff and if you have access to a computer that all can see there's agreat website called www.freerice.com that donates 10 grains of rice to countries that need food for each correct answer. Our cl got hooked on it and donated over 101,500 grains this past year. I hope this helps you figure out some things to do. Good luck and have fun with this!