This should not cause you an issue, but this sounds more like a problem with the O2 sensors than with the intake gaskets. When was the last time you had them changed? If you are over 100k miles without new ones, I'd highly suggest this first.
One way to check your theory for the intake gasket is by using a spray bottle with water (on jet, not spray). With the engine running at normal operating temps, spray the area of the intake manifold gasket. You are wanting to hear a change in tone of how the engine is running. When you find a hole (or leaking area), there will be a distinct difference in how the engine runs. The O2 response being slow is what is inclining me to think of this. As O2 sensors get older, the don't normally go bad per-se, but rather they get lazy. They will continue to get more lazy as time goes on. This will cause you to get increasingly worse fuel mileage.
Other things you can do is to ensure you do not have any leaks in your intake tract after the Mass Airflow Sensor. This could be anywhere between it and the head, where the air/fuel enters the cylinder head. Check all vacuum lines/hoses attached to the intake manifold for cracking or breakage. Check to ensure the intake tract is firmly and correctly attached to the throttle body.
As I said, running this to the store to pick up parts will not cause you issue, but get this fixed as soon as possible, you darn sure aren't helping your engine any.
