Skulls and shockwaves are vaguely useless to carry around.
They're not bad, it's just...you could be carrying something you use more than once, that's more likely to save your life. Skulls are pretty much Mortuary/Limbo fodder for me; If I'm not keeping them for that, I just use them the first convenient spot for a small heal or berserk(and I just pick up Fire ones to register them.).
Shockwaves just strike me as kinda bad(not on paper, just...they don't compete well with the other uses for a slot. 50 average damage over rad 6 is basically a BFG shot with the range of a knife throw. Think about how often this will save you). Actual Hellwaves are a good Phase substitute(you can often use them in many of the same situations you'd need a Phase), but they're pretty rare.
A lot of new players tend to carry ~10 medkits, which is a lot more than you should need.
Hey, I go up to seven or eight sometimes. :| But I like my safety nets, and often sacrifice weapon options for more medkits. And of course, a really durable armor means no armor spares needed, which means more Medkits.
What I'm saying here is that I really like Medkits.
The trick is mostly that you should never carry Small Medkits after the first eight floors-they're not even that great there, unless you're on ITYTD! or N!. That's a big newbie mistake; They just aren't that good, at best being better than nothing.
Large Medkits only get common enough to be inventory clutter if you're having a really, really good run, so it's not really that big of a deal anyways.