Basically I'm looking for a way to allow logged in users to re-order their last order. Has anyone ever tried this before in Expresso Store?
There's no built in way to do it. There are lots of possible complexities, like the fact products ordered in the past may no longer even exist!
If you want to do this, two possible ways come to mind.
You could use the standard add to cart tag along with the orders tag, to add multiple products from a previous order to the cart, all at once. This would require some clever templating, especially if your products have complex modifiers.
Alternatively, you could use PHP and create a simple plugin, which loads a previous order and adds products to the current cart. This would probably be cleaner, but requires some knowledge of PHP.