Hoarding is something most people struggle with, but it had various degrees. Yours seems to be "personal hoarding"--the type where anything involving you gets stashed.
I actually just got over hoarding awhile ago. We're going to get my room repainted, and I needed to clear out a lot (and I mean a lot) of stuff, so I decided it was time to make decisions I hadn't before.
I brought a giant black trash-bag up into my room and I started rifting through drawers. I found probably six hundred old drawings of mine. They were nice to look at then. A reminder of how much progress I've made since I was little. But will they come in handy later? No. Are they clogging up my room? Yes. Are they ultimately doing me more harm than good? Mm-hmm. For sure.
Lots of people suggest that you throw things out without looking at them first so you don't get attached. Don't do that. It will cause you anxiety. Treasure what you look at, and then put it away in the trash-bag. How many times do you go through your drawers? If you're like me, probably only twice, three, four times a year. That goes to show that these things aren't really as important as you make them in your head.
Once you clear things out of your room, you'll feel so much better. But don't push it. If something is really pulling on your heartstrings (that ugly sweater that your aunt made for you but that was knit with tons of love, maybe?), don't push yourself to get rid of it. The occasional saving isn't bad. Who knows; maybe you'll get rid of it later?
The more I started throwing things out, the easier it became. Before long, I was just tossing things carelessly. You might not be like that, though, so let's start off with a first point.
1. Trash anything that reminds you of you before your transition.
I actually tossed birthday cards, gifts, and personal items with my feminine name on them. It was just too painful to keep in my room.
2. Keep anything personal if you need to.
Maybe journals, reminders, and calender pages. Cards can fall under this category. However, a grocery receipt is not personal. Especially if it's been eight months since you bought the groceries listen on the receipt.
3. Ask a friend.
If you're having a hard deciding if you should trash something or not, ask a friend if they would toss it if it was there's. You can even PM me and ask me about it--I'm open.
I hope this helped. Any questions on anything I said? Ask away.