I +1 this suggestion.
I saw somewhere an NPC that would give a certain item an special attribute, like for example lets divide it in colors, red, blue and green.
Legends:
Red = Offensive equipment.
Green = Defensive equipment
Blue = Extra.
When you give one item to the NPC it makes that item one of those colors [tags it] and with the color an exact different ID to the others.
So here is an example:
In your inventory right now you have 8 armors.
2 of them are Red.
4 of them are Green.
2 of them are Blue.
And you have them distributed on the following keys: f1 = Red, f2 = Green, f3 = Blue.
when you hit the f1 key you will be just going through the 2 red armors instead of going through all the 8 different armors that you have in your inventory.
Let me know if you got lost somewhere.