Reordering can be done from the history page, near an item that you've ordered you'll notice a Reorder button. This button will copy all the settings from the previous job and even copy the job files if that setting is turned on and the files are available. There will also be an indication what the original job and item were to easily identify reorders. Below is an example of someone re-ordering an estimate they had previously placed.
In addition to a reorder you can also Duplicate items in a cart, this helps if you need to order multiple items that use the same form with just a few changes. To copy an item find the "Duplicate" button on the left side when looking at your cart. This will take you to the form with those duplicated setting and from there you can edit it further and add it to your cart. Below is an example of someone duplicating an estimate and changing a few of the details of the order before adding it to their cart.