Threading pasta onto bootlaces. Garden chalks for paths and walls (washes off really easily). Small garden tools to 'help'with leaf raking, digging, etc.
A large empty cardboard box and a packet of colouring pencils/crayons - my twins would sit in a box for hours colouring it in.
A large box with ball-pool balls in it. A large empty box with a blanket and a bowl of low fat popcorn for 'movie' night (often became nap time!). Small dolly and pram for walks - dolly can be washed and have his/her hair done, wrapped in a blanket for walks, have his/her clothes washed in the sink while stood on a chair, then pegged out on a low line - an eminently unisex activity loved by my girls and their wee (male) cousins. Decorating cut out crowns with stickers (any craft shop wll be able to supply coloured and shiny paper and stick on jewels).
Baking, very basic woodwork, supervised science experiments - what happens if we... Encouraging reading, writing, counting etc.... every activity can be a teaching/learning experience - little minds are sponges and soak up everything.
Basically, embrace your inner child!