Bag management

I've posted about what to shop for your coins.

Now, what are you going to do with your 1000 slots?

Each player will find a balance between gym battle capacity and the sustained ability to catch pokemon when pokestops are (relatively) few and far between. This balance is individual because of our personal habits and where we live.

If you're always short on either side (can't participate fully in raids, or run out of balls to throw), you need to rebalance your bag. That's done by throwing away a lot of the stuff you never run out of whenever you have the opportunity to rapidly replenish your bag.

Each side also has an internal balance, or rather, you should aim at better quality items. Let's say you always want a minimum of 100 potions and 100 revives in your bag, but no more than 150 of each.

You're currently sitting on 150 potions, so all is perfectly fine? Maybe not. If 70 of those potions are 20 hp heals it might be a perfectly sane action to discard fifty of those. Obviously you won't collect 50 potions of higher quality, or even 50 potions at all, but you'll gradually have higher and higher quality items if you just dare to throw out the crap before hunting pokestops.

Now the game has its own balance as well. Kind of like a pendulum. When you're grinding pokemon you're less likely to to do gym battle, and vice versa. By planning your game you'll have an even better experience.

Spending two hours by lures with friends before a raid? Just stack up on all the revives and potions you get. Everything. You'll be able to spend at least one gym, maybe two, not using a single item of your high quality gym material.

The opposite is also true. If you're planning to go pokemon hunting after some gym battles it might be a good idea to allow yourself to go dangerously low on gym material. While you're hunting you'll slowly deplete your pokeballs and razz berries while at the same time slowly collecting items you can use during your next gym battle.

Last, do you revive and heal everything after a battle? Why? Do you need those pokemon soon?

If not, just let them be. You can revive and heal them one after another while you're hunting pokemon, and especially when you're hunting pokestops. Suddenly all those crap potions come in handy because your method of throwing them away is applying them to an injured pokemon. This is possibly the most efficient way to ensure that you keep a high quality gym battle items as possible in your bag.