great summer idea-ice eggs - Freeze balloons filled with water and small toys. Cut balloon off and play with eggs outside. Provide spoons for cracking ice and digging treasures out. - looks like a great activity for hot summer days!
How to keep a child busy for hours in the summer: DIY: Giant Ice Cube Awesomeness - filled with plastic animals, dinos, and such. And I'm sure you could put in food dye before its frozen to color it like the ice block in the photo.
Before a trip to the beach, hot-glue double layers of foam letters, numbers, and shapes to the bottom of kids flip-flops so that they leave fun prints when they walked in the sand. Just remember that the prints will be a mirror image!