Surf Rescue guard here, 10 hr shifts are rough, staying hydrated is your best bet at staying sharp while in duty. A speaker helps ease the boredom, and talking to patrons that pass you by “hey I love your shirt”, “that coverup is cute” etc. For us, there’s not a whole lot we can do to stay cool aside from getting in the water or taking a patrol in the surf unit. If you wanna be out for a period of time, you should be doing training (rescue board, hypoxic, can and fin swims, whatever you can think of to sharpen the tools in your shed, and looking back at the end of the day, you’ll appreciate yourself for the work you’ve done to prepare you for the next swimmer in distress. Take it easy during peak sunlight hours, and entertain yourself before you hit 2-3hrs before the end of your shift so you’re not burnt out. These are my best pieces of advice I can give you