It's best if you don't worry about this too much until the end of the game. Getting the Drone Teleport and Red Coat allow you access to the entire map, as well as making some difficult sections far easier to get through. You will need to collect 13 Health Nodes
. While this can be collected on its own, you will need to do this on the way to finishing the 100% Items trophy.
The 100% Items trophy in Axiom Verge worth 230 pointsAcquire 100% of all weapons, tools, upgrades, and notes.
There are two things that need to be kept in mind. 1) If you find a secret world, there are power-ups and upgrades that can be collected. These don't count towards collecting everything but they may still appear in your inventory, throwing off your count. 2) There are Small Health and Power Nodes. When you collect enough of them, they turn into large ones in your inventory. Example: You have 9 Large Health Nodes and 4 Small Health Nodes in your inventory. After collecting another Small Health Node, your inventory will reflect that you've collected 10 Large Health Nodes and 0 Small Health Nodes.
If you hit a dead end where there should be more room, try to teleport through what look like solid walls.