How long are you there? Just a day? Short term / longer term?
Short, sharp inputs. There will be a teacher’s plan on the table I assume when you arrive.
Try and keep input to 10 / 15 minutes tops and lots of interaction. I teach reception - i then send them off for child-initiated play and call over groups at a time to do the work, and my TA does the same or hears readers.
If they’re getting restless, have some movement breaks ready on the board - the Learning Station on YouTube (if it’s not blocked) has some good ones like “shake your sillies out”.
Those little whiteboards are your best friend - hopefully they’ve got boards and markers, they’ve been a staple in every EYFS class I’ve been in. Use them to run through phonics - all the children have their own, run through sounds and High Frequency / Sight words. Also use them for a ten minute number work filler - practice number formation, simple addition - have children in a circle on the carpet with Irene’s in front of you as a visual for some addition sums / taking away, get them to write the answer, or full number sentence. Got a gap to fill? Get those boards out and improvise with the above. “I bet you’re not clever enough to know these sounds!”.
Special stickers that are yours will be highly approved I’m sure.
My class LOVE telling the supply their routine - this isn’t necessarily across the board but giving them the power - ask them to explain their playtime routine etc. I doubt you’ll be alone if it’s reception.
Be ready with some songs and stories if needs be. Do you have any idea on topic? You could bring in something to show them or your favourite story or such.
Best of luck, I love reception. Remember, as a days supply if that’s the case, you can always just challenge them to construct something / “cook” something / draw something as a team or as a little contest if you need to rein them in.