1. "Open when..." letters

"Open when you're having a bad day," "open when you miss me," "open when you need some inspiration"—the list goes on. Writing your boyfriend or girlfriend a set of letters is thoughtful, romantic and a gift that keeps on giving. If you're in a long distance relationship, this is perfect for you!

2. Frame your "firsts"

If you're a sentimental couple, consider making a keepsake of your "firsts" together with labels and locations.

3. Funny coffee mugs

It's one thing to gift a coffee mug, but a personalized mug that you decorate yourself is on a whole different level. Make your S.O. smile with a silly coffee mug made just for them.

4. DIY Christmas ornament

There are so many possibilities with this one: make a keepsake out of movie tickets, your first house/apartment key, wine corks, your wedding invitation and so much more. This gift isn't just timely with the holidays, it's a keepsake you could hang up every Christmas together.

5. Date night in a box

Put together a box with the tools for a future date night together—a bottle of wine, chocolates, a movie, a cozy blanket, and you're all set.

6. Homemade art

If you're the artsy type, maybe a homemade piece of art is the perfect gift idea. This could be anything from a collage, to a painting, to a framed image of you two.

7. A "favorite things" bag

Show your S.O. how well you know them with a DIY "favorite things" bag filled with things like their favorite candy, a gift card to their favorite restaurant, a piece of clothing from their favorite brand, and so on.

8. The classic scrapbook

You can never go wrong with a scrapbook. Perhaps the ultimate sentimental DIY gift, there's no way your S.O. won't be blown away by something so thoughtful.