In my opinion fresh and high quality uniform gear should be a given, not a bonus.
Cold cash is always a great way to motivate people. But here are some other practices I use to really build a strong relationship with my guys
Find out what things they want but would never buy for themselves and get it as a surprise gift. Power tools, guns/hunting gear, gaming stuff ect. If you have trouble figuring these things out, ask their co workers or even message a family member telling them it is a surprise!
Notice one of your guys personal truck has bald tires? Write down the size and have 4 new ones sitting in the bed of his truck on a friday.
Guy shows up with windows down in the summer? His AC is probably out, offer to have it fixed while he is at work.
Food! Food! Food! Try to buy them a hot lunch at least once a week. $15 Per meal this is really a small expense to keep your guys happy. Bring them cold sports drinks often if they work outside! Snacks and little candies are always good too.
Most guys are simple creatures and just want to feel like someone is grateful for the sacrifice they make every day, I know because I am one. Most of these ideas I came up with working at my previous employer before I started my own company and they have had incredible results.