Whew! Lots of good advice.
Water vs sugar'd drinks: Pure water doesn't absorb as fast in the gut as does water with some sugar in it. 7% sugar works out to half strength for most things. I like to put a single can of OJ in a 1 gallon thermos. Buy gatorade powder, but dilute it with more water than they say. Cool water is better than cold.
Foot protection. Here in Canada you can get boots that are 'crush resitant' but not steel toes. They will take the same impacts, but aren't nearly as cold. I prefer the nylong top boots for summer use, as they are cooler, and years as a canoe guide I really don't care if my feet are wet.
Shin protection: In really hot weather employees like shorts. But as some one pointed out shorts plus weed-eater can be painful. So as a option, use chaps or shinguards. The shinguards used by orienteering nuts work great. (These guys go through brush at a dead run...)
Spare parts. Never buy one of anything. If you found you needed it, buy 2. One is in stock either in your truck or your shop. (Ok, maybe not for the 24 Hp engine...)
A friend of mine has a sign on his table saw: "Count fingers after every use" It drives home the point with humour.
I keep several spare fleeces and jackets and raincoats in my truck. I hire a lot of high school help, and they are often under dressed. Also work gloves.
If you are in a hot climate, try very loose long sleave light weight white clothing.