Here's a list of approved actions during first solo's:
- Talking to yourself while mimicking your instructors voice
- Singing
- Whistling
- Whooping and hollering
I know people (including me) who have done all or some of the above during their first solo.
Seriously, don't overthink it too much. Treat it just like any other trip into the circuit, your aim being to fly that elusive perfect circuit. Your instructor might have a last second tip for you as they get out, that is the best advice you'll get and supersedes anything you read here.