Some one time use items are rare like level 4's and 5's but as for the reusable gear, I think they are just common. I figure that Veteran packs will give you reusable gears although it would most likely take a long time to get a level 5. I suggest the support
pack or premium specter packs.
Reusable gear items would be the bottom right of the equipment screen. They can be used over and over. For instance I am currently using extra shield level 4 which gives me 25% extra shields every round as long as I remember to put in on at the start of
my playing. It stays on until you turn the game off.