In Texas, since september; you don't need a permit to have a gun in your vehicle, you are assumed by law to be traveling and that allows carry under the Texas constitution.
Of course this does not apply to longarms, which can still legaly be carried in the gunrack on the back window at any time.... LOL..
Minor quibble... since September, we now have the presumption of travel given by law, but presumption is not fact. A prosecutor could still charge you with illegally carrying a concealed firearm and use the circumstances of your trip (car full of groceries, you were in-between the grocery store and your house heading towards your house, etc) to prove that you were not traveling. You'd have to have a real jerk prosecutor, or a lot of other mitigating circumstances to be prosecuted this way, but you could be.