They would normally do some phonics practise each day, so you need to find out which letters they are on from the TA when you arrive and do some activities around that.
I would plan a story, either to tell with a puppet or select a large book with some pictures that you can turn around and show.
There will be a period of time for free play also, I would have thought.
Maths wise, they are probably practising things like counting in 2s and 10s. You can do this in a circle as a class. Also counting forwards and backwards from 0-10. Standing round on a circle, crouch down to start counting and then jump up at 10, then backwards 10,9,8.....3,2,1,0 blast off!
The TA will be very involved at this age also, so I would ask them about where the children are and what the normal routine is, as at this age the routine is so important and can be chaos if the normal routine is strayed from.
Good luck! 