You know, how those songs you used to listen to when young bring back the memories of your childhood much stronger than you can by yourself? Well, I guess you could use it to your advantage in a certain way.
For the epic Japan trip, I happened to be planning it while kinda addicted to Tamura Yukari's "Endless Story". It's a very fitting song, since it has a cultral feel to it, and it also helps that during the OP of C3, they show the Cherry Blossoms and the characters running through such a forest of Cherry trees.
After a few days I started to associate the song very strongly with the essence of Japan, and everytime I continued to plan for the Japan trip, I'd play that song. Now, listening to it again brings back the great memories of PLANNING for the trip. You might think it's not a good memory since planning is usually tedious, but for this one it was really exciting. Don't forget memories carry emotions with them, and because I wasn't feeling that the task was extremely tedious, and on the flipSide (get the unreleated pun?) I was actually enjoying it and feeling really excited the more I planned it, the memories it brings back is really awesome.
The conclusion of the trip (the video + photo montage that I did) was played to the song of 胸の行方 (mune no yukue), which has a nostalgic feel. I picked that since a few years down the road, I'd like to look through the video and feel the nostalgia as well as the strong friendship amongst the 5 of us, and the awesomeness of our 19-day trip. Currently, I can sort of feel it already, but like cheese, wine, and all the good stuff, it needs to age a little more to give it a better flavour so to speak.
So next time you want to mark a really awesome occasion, (that occasion needs to be long by the way. A single day will usually not build a strong enough link. So) you might want to pick an appropriate song and keep playing it while doing that activity. After the conclusion of the activity, try waiting a couple of days or weeks, or even months, and then play back that song. You'll find that you've managed to successfully link them together. YMMV of course, so do it in the way that suits you best!