This is very important. Try to stay aware of your motor functions and how you look from the perspective of someone else.
Slow, groggy looking behavior is much less stigmatized than the sort of animated, hyper focus that only comes from using hard stimulants.
Avoid close quartered, face to face conversations. If you can't, stay mindful of your eyes. Avoid rapid eye movements, blinking too much, and as hard as it will be, DO NOT FINISH SENTENCES FOR PEOPLE.
Cocaine being what it is, I wouldn't advise doing more before your shift.
It is not meth, a little will not go a long way (especially day 2 maintenance dosing) and you will end up making repeated trips to the bathroom to redose, coming out each time with an inexplicable case of the allergies.
Last resort, the most effective and immediate fix if you're unable to call out, are gonna be Amphetamines.