Simple stuff.
Maintain a flag: Did I touch some probably disgusting surface [trolley/phone/mouse/keyboard/door handle/seat/other people/whatever]? If so, do not touch mouth/nose/eyes/wounds/food until hand properly washed.
Is some idiot coughing or sneezing his heart out? Shut my fuck up and breath through the nose.
Consider everything brought home from supermarket to have potentially contaminated surfaces (checkout-conveyors are disgusting).
That kind of thing. Really just a question of habit. Not in any way going Howard Hughes. I once had a girlfriend who did that (going slightly bonkers from studying medicine (but fine today, and a practicing doctor, better for the experience)), and am well aware of the danger signs.