R.Y.
I would say bring some toys of his own. We have a bag of sand toys for my 3 year old son with a few sets of pails and shovels so he can play with other kids and there is plenty for up to 3-4 kids (sometimes 3 of the same toy is easier than 3 different toys!). Most kids old enough to talk well will ask to play. But I do have to sometimes ask other kids to give something back (or prompt my son to ask for it nicely). He is pretty good most days. I am also teaching him if a toy is left out anyone could use or take it (if he doesn't want to share it, put it away). But a kid under 2 can't understand that yet. Also, at around 18-20 months he was going after the same type of toy repeatedly (little trains like Thomas) and we got him a few in order to stop this and it worked well--he still plays with them.