I feel this too. I literally have a film 35mm camera, with normal and zoom lens sitting on my coffee table begging "Why am I still here?!?" (Truth be told it's there because a decent yearly bonus meant I finally bought a DSLR, so it really is useless now and I've been looking up ways to donate it or otherwise not trash it)
I'd unpack it ALL, and force yourself to repack it if (and only if) you can answer: "This is useful because..."
Consider what you can have digitally rather than in physical form (can you scan papers, etc.)
For the papers from school, you can reteach yourself that stuff from books (from the library etc.) It's not like the knowledge goes away with the paper... and it will be trivial the second time around... Scan or photograph the syllabus or text book covers so you have a digital copy and know HOW to find suitable materials on that topic later if it ever becomes an issue. That's your "mental lifeline" to getting the re-education on that topic and lets you get rid of the physical materials. Note also how this shows the "use" is the info in the book and not the dead tree portion... so think critically about the "useful" and realize there is a scale (and eventually you'll be able to catch yourself claiming something is useful that really isn't)
For other physical things, like books, I subscribe to some of what Zikoris says, but it's hard. I sometimes do them in stages. Pull out your books and separate the favorites, then make other piles of "good but not the best", "might be willing to get rid of this", "really not great". Maybe a handful of categories if you need that many. Take the lowest category and stack it near your exit door. Leave it for a bit (more than a day). Stack them so you can read all of the titles/bindings as you go by. Look through it after that and make sure nothing is "I must keep this or else". Anything that goes back into the save bucket needs to be swapped for something else. Then get rid of it. Note this process separates some of the emotion - you can safely stack it downstairs without it being guaranteed to be removed from the house... but after a while you've validated multiple times the books are "meh" and the pile downstairs gets in the way and needs to GO. Lather, rinse, repeat (using the same number of categories with different meaning) until the collection is down to a smaller size... maybe limit the keepers to what can fit on XYZ bookshelf in your house.
Do you wear the band shirts? If they are in the standard rotation, they will get worn out. No biggie, IMHO. If they are collectors items, maybe see if you can get them made into a quilt. At least then they are a blanket and not just a pile of shirts... For clothing, I have a 2/2 rule. If I haven't worn it in 2 years, it gets disposed of, unless it's a category I have <=2 of (think suit for funerals or some specialist outdoor gear).
For the tools, how far are you moving? How much are they worth? How heavy are they? In my last inter-state move, I found out what it cost per pound and was calculating a lot of stuff... literally some items I could buy new for $80 were going to be $58 to move... needless to say, I didn't move the heavy stuff unless it was something where I had an active plan and was using that object frequently.
Also, ask yourself whether the "someday" is because you want the item to be used or because you actually enjoy doing that thing. If it's the former, then that object deserves a home where someone will use it, even if you take a mental hit (from the "I spent money on that and never used it" zone). If it's the latter, then start building a list of the things you actually enjoy doing. Make it a 1..N prioritized list. If something falls down to 5 or 6, do you think you'll ever get to it? REALLY? Because you shouldn't be saving everything, you should be saving the stuff you actually use, and MAYBE (but not always) the things for the 1-2 projects where you will really put the time in "someday" (especially if those items are expensive or hard to get). Realistically, it won't be 5 someday things you'll get to...
When you move and unpack, force yourself to unpack EVERYTHING. Nothing left in a box rule. If it doesn't have a place, it doesn't have a home, and needs to go. This has helped me thin books and kitchen items that somehow had passed the "This is useful" test...