Deadlock

Active reload! I feel like reloading in general takes too long, so this helps alleviate that a bit; the fire rate bonus makes it even better, since when you're in a hurry to reload, you're probably in a hurry to shoot afterwards as well.

I really like quicksilver reload. You assign it to an ability, and using that ability then also instantly reloads your weapon.

That's REALLY useful when combined with something that creates an opportunity to do damage, like a stun or movement ability, which then always comes with a full mag ready to be dumped.

Anything with lifesteal, otherwise the biggest QoL is melee charge for me, never having to reload while dealing with creep is a big plus for me.

Does boots count? I buy Enduring Speed a lot. Melee Lifesteal is really good in lane, I buy it on almost anyone. Majestic Leap is probably the most fun item, but I'm not good enough yet to abuse it and have it pay off consistently.