Recommendations for best toys for 7 month old?

[MummyBerryJuice]

We are VERY short on cash but DS is becoming very bored with his toys (mainly rattles, soft toys, teethers etc) and I would like to get him a few things, probably from ebay, that will entertain and stretch him as well as last for a while.

What would you recommend as your top toys?

If you only get one thing make it a set of stacking cups. Hours of fun!

Ours still get played with by my 4 and 2yo in the bath, in the sandpit, etc.

stacking cups
stacking rings
basic shape sorter (they like the shapes, won't use it as a shape sorter for a good while)
they don't need a lot