I'm a pretty new player myself (about a month) and was really bad about hoarding everything because I didn't know what would be needed for quests and the hideout. Then I stumbled along a spreadsheet from /u/DyGr. It listed all of the items you needed for each of the hideout upgrades. I found it incredibly useful, but decided to overhaul the functions to suit my needs.
Make a copy of the sheet for yourself and you can try it out. As you update your stash numbers in the first table, the upgrades will be highlighted in the second table. As you complete those upgrades in-game, you can check them off, which will in turn update the required number of items remaining. (I've also kept the individual upgrade requirements as a reference, although you don't need to edit anything there. It will update automatically.)
Let me know what you think! If you find any issues or have any suggestions to make it more useful, please let me know. Credit to /u/DyGr for the inspiration and awesome original spreadsheet. If there is enough interest, I plan on doing something similar for the Quests, allowing you to check of the ones you have completed to update the item numbers.
If you want to be prompted to make a copy right away, use this link instead:
