One example I can give you is my copy of Majora's Mask. For some reason I always really liked the boxart of that game. It's nothing extravagant. But for some reason it speaks to me. I've had it on display on one of my shelves for 15 years now. And every time I glance over at it, it brings back a little bit of the feeling I had when I played the game as a kid, and the memories I have associated with it. Including the store I went to to buy the game, the snowstorm outside, and how much of a hurry I was in to get home in order to play it.
Good for you, but not everyone needs physical objects with pretty pictures on it to get in that nostalgic mode.
For example you can put all your favorite pictures (boxart, screenshots, concept art, fan art) of your favorite games in your screen saver rotation... every time it is shown on your display, you can glance over at it, it brings back a little bit of the feeling you had when you played the game as a kid, and the memories you have associated with it. Including the digital store you bought the game, the good feeling that you didn't have to freeze in that snowstorm outside, the happy memories you had with your family instead while the console was downloading the game, and how eagerly you were to start the game, when the download was almost finished. ;)
I'm happy with my physical and digital collections, but don't think that young gamers born in a digital age will get less nostalgic in a few years because they had no physical box for their games. Other pictures, retro reports, emulated/ versions of their childhood-games on new devices, game soundtracks or retro youtube videos will be enough to get them in the same nostalgic mode.