For years, I shot up nightly.
Didn’t matter where I was, I had a small vial, a hypodermic needle and an alcohol swab. I had to have my “fix” at the same time every day, so if I was at a friend’s for dinner I’d take my stash into the bathroom and do what I needed to do.
Sure, I could be off by a short time, but I was compulsive about maintaining the consistent schedule. If that meant that I had to quietly excuse myself from a picnic in order to go to the car and dose up, I’d do it.