In HL2, unlike HL1, it is possible to pick up ammo, health, suit energy cells, etc - so long as you’re at maximum for that resource type.
I’ve found myself stockpiling consumables - picking them up, moving them along with me, throwing them down the hallway, etc.
At one point (I’ve not been doing it that much yet) I had three suit energy cells, two health packs, two grenade shells and some shotgun ammo.
Of course, it’s a pain to do, but it’s worth it for the suit energy cells.