This list I use to use a lot when playing IA:

These gems/necklesses are used for itemupgrades - as per the title - and thus you might want to carry them with you or save them for later:

Yes, this and these two as well:


Red Coral Gem and the 48-sided Garnet are unique; there are three Golden Star Garnet gems in the entire game.

Having such a master list of required gems is useful to know which kinds of gems to keep and which to sell. It's even good to add the maximum numbers of each type you may need in the game to the list so that you don't unnecessarily keep too many of each type in your inventory. (Of course for some of them there is no definite maximum required numbers; for example, the Laeral's Tear Necklace can be used to upgrade protections cloaks and the number you need depends on the number of cloaks you want to upgrade.)

Also, keep an eye on your cash. If you spend too much money on small upgrades, you may eventually face financial problems for the major and expensive item upgrades.