Well, I'm part of the general consensus. Only problem with making the stims "run out" is now you're dealing with a tangible item in relative terms. I'm really not a fan of the "you can use this item sometimes, but only when I feel like it" approach. How is a doctor unable to just look inside the kit and see how many are there? My players are going to be on a strict equipment budget, and this like this makes it hard to manage.
It's not that the character(s) *can't* look inside the kit to see how many there are.
It's that they didn't, thus they get surprised when they discover they've run through the stims in the kit.
If, on the other hand, they did think to check how many stims the medpac had 'on board' then you (the GM) simply tell them there's X stims left in the kit, and when they run through that, it's done until they've had a chance to refill/refresh the kit.
And a stims don't take care of critical injuries. Accumulating *those* is what makes combat risky for PCs.
The assumption here is that all wounds are given the same amount of stim pac bacta. Likely some wounds take more than others. That's how I'd describe it to my players.