Here is one tray with LOTS of learning opportunities
Coloured sand, astroturf and ladybirds for crafts.
Numicon is amazing for understanding doubles.
You can use any counters you have at home. Place an acrylic (safe) mirror near until you see a full reflection of your counters. For example you will have 3 counters on a tray and 3 in a mirror 3+3 now, count them all together.
I used a paint tray and pom poms. I use that tray a lot but not for painting :D