
Not saying that this is a great card, but it's a fun challenge during deck buildung (and upgrading) and makes every opening hand draw exciting. I had some success with Geared Up and Rex Murphy, but most things I noticed should work with different investigators as well.
1.) Try to find cheap items rather than pricy ones. Costs of 1-3 are the right spot. In fact, my Rex' deck contained no items more expensive than 3. You should be able to pay for ALL your items from your starting hand.
2.) Upgrade your items as soon as possible. Not only will it makes your early game more powerful, upgraded items also have better icons for committing into skill tests. Sometimes they get cheaper too or have abilities.
3.) Mulligan hard for items, even if it hurts.
4.) Because you pack lots of items and often two copies, clever ways of discarding copies (with bad icons) from your hand or from play helps your mid-/late-game where you already have your assets out. Examples are Cornered, Occult Invocation, Blood-Rite, Act of Desperation or even mitigating discard effects like in Divination or Mists of R'lyeh. I paired Geared Up with Forced Learning to get rid of double items during upkeep. Items which go away or go empty like Disc of Itzamna or Scroll of Secrets allows you to refill the slots. Investigators like "Ashcan" Pete and Wendy Adams (Hello In the Thick of It / Versatile) for discarding cards from hand, but also William Yorick and Dexter Drake should find ways to utilize left over items.
5.) Remember that you still can play fast cards or use actions on your items in turn one. That's why I love Eon Chart, because as a item it grants free move and/or investigate actions right at the start. The tabooed Scroll of Secrets (all versions) helps you refilling your hand for the mythos. Fast Events like Working a Hunch or Shortcut (2) also are playable in turn one. Funny: If you happen to find No Stone Unturned (5) in your opening hand, you could play it right at the beginning of the investigation phase (but before your turn begins) to catch Schoffner's Catalogue, a critical weapon or signature item or Backpack (2) for playing it for free with Geared Up.
6.) To get the most out of it economy wise, non-fast items comes to mind. But don't be afraid to include fast items like Magnifying Glass, Ice Pick or Segment of Onyx. You will get the resource reducing anyhow. Also fast items don't slow down your mid-/late-game if you draw them late.
7.) The most difficult part for me to make Geared Up work is to find items with different or no slots. Because if you have a pile of cards which required hand slots you'll end up drawing them as essentially dead items slowing down your game. Relic Hunter is a possibility to play more accessories. If you look closely, there are neat items with no or odd slots: Dream-Enhancing Serum and Talisman of Protection just use arcane slots, if you have no spells to prepare. Slotless mentions are Handcuffs, Mk 1 Grenades, Bandages, Tennessee Sour Mash and Liquid Courage. And then there are the great Schoffner's Catalogue and the footwear items, of course. The true winners in my Rex Murphy deck though were 2 Strange Solution, which I upgraded with the help of Into the Rabbit Hole and Shrewd Analysis. 3 Segment of Onyx (also slotless) were fun, too. You shouldn't play much body slot items, because Backpack is the best option here (if it works with Geared Up, playing the item assets one at a time, which I think it should). Once I were able to play all items from one Backpack, followed by another Backpack.
8.) Be aware that there could be a few locks in scenarios, but also cheesy benefits to consider. In Curse of the Rougarou I started the game at a location were I was not allowed to play any assets at all. If you use the tarot deck from Return to Circle Undone, there are all sorts of silly interactions: One tarot card that forbids to play assets turn one, another steals slots or cards in your opening hand, starting resources or your mulligan. On the other hand, “2 fewer actions” don't hurt you at all, and 2 additional mulligans or 2 additional cards in the opening hand get very powerful.