There are so many options that you can do with this idea. You could make a bulb every year and choose one photo that summarizes the best thing, whether it be a vacation, family outing, birth, engagement, wedding, graduation, I mean the list seems endless.
All you need is a bulb, plastic or glass, whatever floats your boat. A picture of the memory you want to preserve (I printed a 2x3 picture). And the filler that fits with the theme of the picture.
The photo on the right is an ornament that I made for our in-laws who celebrated their honeymoon this fall. I went for simplicity. The colors match the blue decorations on their Christmas tree and represent the pretty blue ocean they experienced on their honeymoon. Now if it weren't winter and I could get my hand on some, sand would also be a great bottom filler, or shells would work great too. If it's a winter photo adding fake snow, sugar, salt or pine needles is an option. You have to be careful how much you add since you don't want the bulb to be too heavy when you hang it. You can add more details on the back like the location, year, etc. using a marker, glitter stick etc.
Depending on the time in your life, it will guide your ornament making. For example, right now people my age are getting engaged, married, honeymoons, having their first child, and first home. Lots of firsts. So these are a thoughtful and money savvy way to show your support for the couple as they go through their BIG life changes.