Better to mix oils than run a quart low. This would apply either to different brands / same viscosity, which I personally don't think is all that big a deal - or to different viscosities.
It would be best if, in a pinch, you had to add a quart of - say, 5W30 Pennzoil to 2 1/2 quarts of 20W50 Amsoil - to change all 3 1/2 quarts including filter as soon as possible. Not an emergency, but advisable to do so.
In no case would I knowingly run more than 1/2 quart low, certainly just because I didn't have the same oil to put in with me. And good advice to travel with an extra quart, if you can. Not really an option on my V-rod but I always do on the SERK.
Oh, one more thing. Using a quarter per 1000 miles is far, far from normal. Unbelievable what some dealers will call "normal." For reference, I've used a total of 1/2 quart in 10,000 miles. And honestly, I'm not even sure if the 1/2 quart was burned or a case of getting shorted the half quart at the 1000 mile service. Last oil changes I've done myself & not seen a drop burned.