A really simple toddler activity is to grab a bag of clothes pegs and let them sort them! My 2 year old and 10 month old played for about 45 minutes this afternoon with this activity and all it required was a bag of pegs and some plastic plates (bowls or any container will also work). All you need to do is clip a different colored peg onto each plate or bowl and let them sort them into colors. It sounds so simple, but it honestly kept them busy for ages (to be fair the 10 month old wasn't really sorting them, but the 2 year old did quite well!).
Tip: Try and buy the pegs that don't have any metal parts in them - much safer and they last a lot longer.