The answer is....
Equipment list
Sets of subitizing cards in enough envelopes so each pair has one.
One small whiteboard and marker
Explanation
Prep prior to activity:
Divide class into pairs. Write the pair's name on the envelope. Hide the envelopes around the playground.
Gather students together and tell them their partner. Teacher writes a number on the whiteboard. On the signal, student pairs search for their envelope and searches for the subitizing card that represents that number. They bring back the card and as a whole group discuss whether it represents the number on the whiteboard.
Variation/progression
The card content can be different:
base ten representations (conventional and non-conventional)
expressions ("Find the expression that represents 48 - options 38 + 10, 23+25, etc)
fact recall ("Find the answer to ____". Or "Find the question that has an answer of ___"