One of my favorite, laziest crafty quickies is the braided garland: I can whip one up in just a few minutes. I love being able to customize my own colors for the changes of the seasons, and the braiding adds a crafty punch.
I use paper ribbon/raffia, because I have a lot of it on hand for wrapping orders, but Ieftover yarn also works well. Cut three strands 3 to 4 feet in length, depending on the length you want. Keep in mind that it will be a bit shorter than that after the braiding. (Also, if you use yarn, double or triple up on the strands to make the garland thicker.)
Tie the strands in a knot at one end, and secure with a safety pin to something sturdy. You can do this the 80s friendship bracelet way, where you pin the end to your jeans, or connect the pin to a large binder clip & attach that to a shelf or stable piece of furniture. Just pick something that won't move, because you'll need to keep the tension tight. Braid until you have about 6 inches of paper ribbon left, then tie a knot identical to the one on the other end.
Hang it horizontally for a banner effect, or vertically for an up-down look. Use tiny clothespins or last minute washi clips to attach greeting cards, postcards, photos, artwork, and any other little whatevers you want to display. Or -- use it old-school style for the coolest wrapped gift in town.