If it's not something you're committed to doing right now, it belongs on Someday/Maybe.
If you are committed to doing it now, it could be an action, but it could also be a project. If you know exactly what product you want and the local store where you want to buy it, then it's a simple action on @Errands. If it's not that simple (i.e. you're not sure exactly what kind of box you want and/or exactly where you want to buy it), then it's a project. Actions might include surfing the web to find what you want, surfing the web to find the best deal on the box you want, calling a local store, etc.
Some things that seem very simple intuitively are in fact projects because they take more than one action to close the loop. Don't put projects in disguise on your action lists--they will kill your system like a cancer.