For the first two, make sure it's something meaningful. I've gone full Marie Kondo as of late and put a lot of emphasis on things that hold a distinct memory for me. It's very easy (and I did this early on) to buy all of the swag. Just make sure you have an item or two from each squadron that has some meaning for you. Patches do the trick for me, and can be neatly displayed. Some goes for deployments or other big events. I have one of those cheesy glass, colorful chandeliers that they sell all over the middle east. I have no doubt they're mass produced in the hinterland of China, but I can remember clear-as-day where I was and who I was with when I bought it in Bahrain. And it looks pretty cool in my home. Make sure you have good photos with your fellow JOs during all stages of your career. I have lots of bullshit photos from nights out drinking, but vanishingly few photos that feel staged in the moment (i.e. posed on the flight deck in front of a jet) but are pretty cool when you look back. Take the time to get a real photo.
I started hand-writing my logbook during GTI and wish I'd started that from the outset. In both my GA and military logbooks I write short notes on what happened during the flight. Not all, but definitely on more important flights. Handwritten logbooks look more authentic, especially with my line-outs because the old-school logbooks they provide don't line up neatly page-to-page.
For unsolicited career advice, I always go back to what the XO of VT-22 told us before winging. You'll get lots of shitty little jobs throughout your career (i.e. you're the SLJO). Make sure you are the best SLJO ever, people will notice, and you'll go far.
EDIT
When collecting memorabilia throughout your career, remember that you may have a wife/husband/civil partner/cohabitant in your future who does not share your zeal for Navy/deployment kitsch.
