Creating a Keybound inventory

I simply wish to press V and open my Gui, let it store items under a tag, and remember those items are in there next time you hit V. Forums have said to use capabilities (no prior java knowledge) and one said to use Itemstack variables (couldn't figure out how they work) I'm familiar with programming, just not java. if theres any way I can do this with procedures and variables that would be amazing. because the equipped item will enable other in game features later.