I learnt to be quick in my thinking and have a few things up my sleeve that enabled me to interchange quickly.
If activity allows:
When seated: and under supervision by you:
Colouring by numbers ( focuses the mind in the early stages of alzheimers disease and their attention) for periods of time, puzzle books, watching TV only for a short time, mental fitness drills, adding up money, playing cards, doing the times table, playing catch or kicking a soft ball while seated.
Learning how to turn on the computer or laptop, allow them to sit and hold open a bag as you cut down your garden. They need to remain useful and have a purpose or they will go down hill very fast.