Whether you choose to be outside in the hot Sun, or need to be, it can be dangerous for people with health concerns and/or wheelchair users like me.  I use/sit in a black wheelchair and can't sweat (due to high level SCI) -- the solution?  

Buy a plastic spray bottle and fill it with water.  It's a portable mist machine.  That helps me tolerate hot/sunny conditions.  We went to a college football all-star game in Orlando in January a few years ago; it started about 1:00 p.m. and was 85+ degrees and sunny.  There were quite a few wheelchair users attending (the Buoniconti Fund was involved with the game).  My Dad went up and down spraying people in the wheelchair seating area -- one guy was dressed in all black, he was roasting -- and could've had big problems.  My Dad refilled the spray bottle several times (need to spray liberally and relatively frequently if you have health concerns, especially if you can't sweat; we keep a spray bottle in my van).  Try it -- it's inexpensive and could be a life-saver!

Even if you're able-bodied; the mist will feel good to you too!
 
Bill Miller :-)
C1-2 Quadriplegic with a 221 High Bowling Game
Co-founder of Manufacturing Genuine Thrills Inc. d/b/a MGT
My blog: http://powerwheelchairusers.blogspot.com
Business website: http://www.ikanbowler.com
Personal website: http://www.lookmomnohands.net