What items in Pokémon Go count against item storage limit?

The simpler question to answer is "Which items do not count against item storage?"

The simpler answer is gifts and stickers.

Incubators count, but their item count is found in Pokemon storage, in the eggs tab. You must click on the incubators icon to bring up your incubator inventory.

From a tally of my current items, the following are all counted as 'items' in regards to your item count:

• Potion (all types)
• Revive (all types)
• Lucky Egg
• Incense
• TM (all types)
• Rare Candy
• Star Piece
• Pokéballs (all types)
• Lure Module (all types)
• Berries (all types)
• Infinite Incubator
• Purchased Incubators and Super Incubators
• Evolution Items (all types)
• Camera
• Raid Pass (all types)
• Premium Battle Pass
• Mysterious Components and Rocket Radars
• Mystery Box ^*

_{^* The Mystery Box does not disappear when used, and is still counted even when not available for use. It is re-loaded when you repeat the procedure connecting to Pokemon Let's Go on a Nintendo Switch.}

Gifts do not count towards the item total. (Neither do gift stickers, but they are not shown in the items list)