We have the same issue, since there are just two of us as well. I keep it whole, wrap it in foil, then a zip bag. If we want a few slices, I'll slice it cold, then reheat in a covered pot with a tablespoon or so of beef broth. Heat it gently -- you don't want to cook it, just warm it. I'll chop some for tacos and reheat in much the same way, except adding some barbecue sauce (cole slaw and jalapenos in a corn tortilla -- Yum!).
One of my faves is to make a "Tipsy Texan" which is the only sandwich served at Franklin Barbecue. Chop the brisket, heat it with some of Franklin's Espresso Sauce, split and grill a Texas sausage link, stack it all on a large roll with slaw and pickles -- devastatingly delicious.
Jeff