Splitting injections: https://clusterbusters.org/forums/topic/2446-extending-imitrex/ Or, ask for a prescription for vials and syringes so you can measure out your own dose.
There's a lot of caffeine in energy shots (the smaller things like 5-Hour Energy). Not as much in the standard bigger drinks (RedBull). You would probably do fine just brewing some coffee and keeping it in the fridge.