DIY Sand and Rock Box by FSPDT. Gdjk -> made this with toilet rolls (aka tunnels) and moon sand instead of play sand. My son loved playing with it. The moon sand cleans up nicely indoors but play sand will be easier to play with when using the small cars.
Make fishing boats out of cardboard boxes, lay down a blue tarp to make it look like water, use a sand bucket to put the fish in and use those play fishing poles with fish that you get in any toy section at any large super store