Here's a little know strategy that you can use at Walgreens to make or save hundreds or even thousands each year. The first Tuesday of every month is what is known as "Seniors Day" where they give people 55 and older 15% off the whole store and 20% of W brand products. Obviously, it would be great to get that discount, but you're thinking "Rob, I'm not 55". Well, neither am I . So let's dig a b…