Playing around at the shop today, I had to utilize a trick which has come handy many times, but it took me many years to even come across this trick. This may be elementary for some of us, but I still think it's pretty nifty.
Mounting the new control box for the CNC mill today, I had a few hard-to-reach bolts on the case which needed a nut on the other side. I didn't have room to hold it with my fingertips, and the nut would fall out of the bottom of the wrench if I couldn't get my hand in there.
A simple piece of electrical tape can help retain the nut on the wrench just enough to position it, and then let go once it's started to thread. Take a small piece of tape and place it STICKY SIDE DOWN on the wrench. The tape is the perfect size to take up the gaps in the flats on the wrench and gently grab hold onto the nut.
Press the nut into the tape, down into the hex flats, and your nut will be retained nicely without falling out.