Not so many options. Numa Creek is in a hole with nowhere really to go. Best side-trip on Rockwall is Numa Peak, easily reached from Numa Pass but that is practical as day trip from Floe Lake only because of huge elevation gain from Numa camp.
Your best bet is probably to spend time at Tumbling Pass. It is a lovely alpine ~1hr from Tumbling creek camp. Stash your overnight gear then can maybe hike up ridge on east side (~2400m elevation), or descend on other side and explore a bit at toe of Tumbling Glacier:
This is looking back where you came from; Tumbling glacier is across, and on far right is nice tarn --source of Tumbling Creek-- you could probably get to.
Descent from Tumbling Pass to Numa camp is quite brutal btw