At that age I stocked up on
paint and the big rolls of paper you get in IKEA and cheap baby wipes to clean up.
Bubbles solution (avoid bubble machines - blowing their own bubbles is very calming, and keeps them busy for ages longer than a machine)
Play sand
Crayons and colouring pages (one page issued at a time. Ditto for sticker sheets)
Masking tape (excellent for junk modelling, indoor hopscotch, lazer mazes)
Cardboard boxes (endless possibilities)
Sun cream, hats
Paddling pool - (also got use out of garden hose and sprinkler, bucket and paint brushes (for painting the outside of the house with water), sponges for washing windows and cars)
Shovels and spades (I don’t recommend burying coins in the garden for them to find treasure unless you want them digging for years afterwards), small trowels for gardening.
Lollymoulds for fruit juice. Also frozen yogurt tubes are great.
Play dough (or ingredients to make) with selection of cutters and toys.
Popcorn
I used to set up an activity on the play table in the morning and leave them at it while I got on with the morning jobs, and prepped dinner, packed lunch and a platter of veg snacks. Then, we’d head out for an activity (park/swimming/library/shop/playground) and have a picnic lunch (in the car if the weather was rotten). Back for quiet time (kept this up as a replacement for naps as long as I could) and then another activity - bit more hands on from me (although the less you have to do for them the better) Platter of veg came out while dinner was cooking to stave off whining. Not a foolproof routine and it was utterly brain numbing but we all survived.