Nah, Insulin is IM, dope is IV.
Sorry, but insulin is actually taken SC (sub-cutaneously) which is in the fatty layer below the skin but above the muscle. However, those ROAs are very close. If the "junky" was into pharms then they may have experience with getting the solution out of glass vials, since anyone that has done this before knows that you don't just stick the needle in and suck it out--you need to use a negative or positive pressure technique to slowly replace the liquid inside with air so it won't explode under pressure.
I have a positive thing to add to the pile, but it's more of a scenario than an actual skill or memory. Once when I was younger I had taken some codeine in the form of Tylenol 3's ( haha yes, that's right, codeine...waaay back when that worked well), anyway I happened to be riding my mountain bike and dirt jumping it. I ended up endo'ing over the bars then detached in the air, lucky for me (sarcasm) I landed back down on the crossbar with my knees and got my legs tied up in the frame and landed flat on my side (no broken bones), I bruised my legs up bad and tweaked my ankle. Obviously the codeine didn't help with the bruising, but it did help with the pain, especially the ankle since I didn't think I hurt it that badly until the next day when I woke up and it was swollen and was throbbing and all I had left were ibuprofen caplets. So, all in all codeine helped "break my fall" as I was kinda pre-medicated for the injury.
Some of these may be repeats, but I will list as many as I can think of.
-Learning how to prepare a shot to take care of yourself incase alone in extremely severe pain with meds (close to our friends insulin example)
-Facing adversity such as the withdrawals and comparing any subsequential sickness to it (the flu now seems like a joke)
-Quick mental math skills (picking up in bulk/dosing in small amounts such as milligrams or micrograms)
-Self discipline (with the most addicting opioids)
-Bartering skills/interpersonal skills (self explanitory/dealing with different personalities and knowing how to read someone)
-***Being fair with or not rude to police (as most people carry their stash to avoid sickness when out and about)
-Learning to drive the speed limit more often hahaha (kind of a joke)
-Eating lots of fiber (learning which foods fit best in your diet, if your financial situation allows this)
-Learning respect with chemicals (knowing that one miscalculation could be the end of your life)
-Leraning sterility or at least optimal hygiene (being aware of micro-organisms that can cause infection which could ultimately lead to limb loss or death)
...to be continued...