Help them with bills?

janey- I certainly hope it isn't laundry! ;)

Hang a stocking at Christmas?

Make their bed

I think it's financial in nature like Texas_Gem but I will specifically say pay their cell phone bill (include them on the parents bill).

make their dentist appointments for them

Send a birthday card.

Terilyn, I like your answer. We still do that!

I say laundry too

My first thought was the same as Janey's. :)

The number may be too low for this, but I'll say: Tend them when they're sick.

buy them a birthday cake