1 Leave them in the item box
Inside most save rooms there is a large box where you can drop items. The contents in this box can be accessed each time you open a similar box.
2 Combine items
Some items can be combined together then take one place. Make sure you combine all the items that can be combined as soon as you have them.
3 Place items where they belong
If you have an emblem or any other item then you can get rid of it by placing it where it should be placed.
4 Fire more bullets
You can free some space by firing more bullets and so getting an empty slot as a result. This isn't recommended, as ammo is scarce in Resident Evil.
5 Fill your health
You can use herbs, first aid spray and first aid box to fill your health. If you urgently need one more space, you might want to allow yourself to get hit in order to be able to use those items. (See Differences between Chris and Jill – Resident Evil Remastered)
6 Use keys to get rid of them
A key can be discarded once you have used it to open all doors that it can open. In the case of small keys, they get discarded once they are used on any door.
7 Place them where you took them
Many key items, especially the ones that fit somewhere, can be placed back in the place they were taken from. You can keep the item in its place then get back to it when you need it. (See Why Resident Evil HD Remaster is a good game?)
8 There is no way to drop items
There is no way to drop items just like you do in other games. The game was designed with that limitation to make it feel more like a survival game.