How might you increase the average spend per customer in each store?

I would recommend finding out the transaction productivity, meaning in an average transaction, is the typical customer buying 1 item, 2 items, or more? The easiest way is to take the total number of units (or items) sold, and divide by the total number of transactions conducted, that gives you your Units Per Transaction productivity.

This is a sure way to increase your spend per customer, just by getting customers to spend on multiple items. You can recommend some "impulse" items during checkout, or when helping the customer shop.

I'd recommend using Vanilla Progress (vanillaprogress.com), it's a pretty easy to use online tool that tracks your sales progress by analyzing a few basic transaction data, it then tells you your performance in spend per customer, units per transaction, average unit sales, etc. with trend charts, snap shot figures, and business performance summary.