I used some paper scraps to cut little squares in matching colors. Then I gave them all to ER. She really likes it and can sort them by color already, we're still working on naming each one's color as she puts them in the right pile. The last time she made me laugh, as she's discovered a shortcut, and has been putting down more than one eraser at a time.
This is a great activity you can recreate throughout the year with different thematic manipulatives to keep the activity new and fresh. When I was teaching I loved browsing Dollar Stores for all sorts of little things to sort that tied in with my classroom's current theme. As they got proficient at sorting by one attribute, I'd add items that had more attributes to sort by and part of the activity would be having the students tell me how they chose to sort. For example, a Halloween time I put out holiday erasers in a variety of designs, they could sort by color, shape, design, etc.
Oriental Trading is a great resouce for a lot of little things you can use as manipulatives for sorting and counting activities, especially if you want them in bulk for a good price. They also have a Hands on Fun catalog full of teaching supplies also at discount prices when you compare them to teaching supply stores. Both have individually wrapped craft kits that are great for parties and are good activities for all those parent volunteers to do at a station during a classroom party.