I'm kind of waiting to see if mens has any better ideas here, but morphine will actually be useful along with power/combat making it so you only take 1 damage for all damage sources, cateye will probably be the same, but thanks to custom effects I can make it so goddamn milk no longer cures my stuff, psycho will make fall damage either not occur or take a lot more to occur along with the usual effects it gives, stimpacks are likely to remain the same as I like what they do already, I know mens wanted voodoo to be sort of like a luck thing, which with vanilla effects is hard to pull of, so he may have an idea as to how exactly he wants to make "luck" happen. I have yet to decide if I'm doing anything with hydra, afterburner, or buffout, although I'll have to look into what I can do with buffout, it may be possible to make melee useful by screwing over whatever you punch while on that drug.
Also expect to see a more refined overdosing system, I know mens has wanted something like this from the beginning, where overdoses are either rare or non-existant, unless you mix an upper with a downer which is now possible to detect with custom effects. These are both subject to change, but currently I have downers as cateye, buffout, voodoo, and morphine, making uppers afterburner, hydra, stimpacks, and psycho.
Keep in mind that with new custom effects, I don't have to rely upon crappy vanilla effects on overdose to screw you over in creative ways anymore .
EDIT: Oh yeah, forgot to mention, thanks to custom effects I can do an addiction mechanic as well as effectively infinite potion effects for addiction until you get it taken care of.