Parking lot worker at home improvement store
People buy big boxes from big-box stores -- boxes holding stuff like air conditioners, minifridges, and other modern cooling devices. So when the people working the lot at The Home Depot or Lowe's load something like a 60lb lawnmower in your truck, they deserve a few bucks.
So, how much? They average about $10 an hour, so with a $10 tip, you might just make their day. And when's the last time you made someone's day? Other than your mom the one time a year you remember to call her.
The Enterprise employee who picks you up in a rental car
When a cab driver drives me 40ft, I tip them $1. When a bartender cracks open my beer, that's at least a buck. So when an Enterprise agent/former NCAA athlete (if the commercials are to be believed) picks me up at my hotel, or friend's house, or wherever, and drives me to Enterprise for 10-15 minutes, that person deserves some cash. There are specials at Enterprise where you can rent a car for a weekend for only $10 a day, so another few bucks isn't going to break the bank. Based on the Enterprise employees we spoke to, they receive tips so rarely that you'll likely get a surprised, happy driver out of the deal.
So, how much? $1-$5