I just make sure the battery is firmly in place. I do this after reading a few reports here with drones actually dropping from the sky due to an immediate lack of power, likely because of an unseated battery. I feel pretty sure that after I snap it in place, and verify, that it's good.
I stop at that because adding a strap brings in a new potential issue, something that could come off and get into a prop, with the same potential effect of making the drone fall out of the sky. At this point I have to ask which is more likely - the battery unsnaps itself, or the strap comes off somehow. Since neither seems more likely than the other to me, I just leave it as-is.
A strap is probably a good idea but just raising the point that sometimes (maybe not in this case but sometimes) a cure is worse than the original thing you are trying to cure.