The cooldown trick = Items cool down slower in backpacks. When you're in base, or hanging out at a secret shop, move any items on cooldown into your main inventory. This generally gives you only a few seconds.
The tango trick = The side shop also counts as a shop. You can freely use consumables out of your backpack with no drawback as long as you're at the side shop. This is most important with tangos, salves and clarities during the early laning stage.
The shrine trick = The trick of putting mana pool items into one's backpack when using a shrine is well-known; it slightly increases how much mana one gets from a shrine. Both offlane shrines are barely within range of a secret shop, so be sure you're standing on the correct side of the shrine when you put those items back into your main inventory.