What to do when waiting for everyone to finish their exams?

Okay, so i know this is a really strange question but sometimes i finish my exams rather quickly and still have 30-50 mins left of the exam, during this time i check over my work but what else can i do? i get sleepy very easily and im scared that i might fall asleep so what can i do to amuse myself during this time? nothing rude guys, its a sqa exam, hehe,xo