This is your best bet. They don't go bad (as in breaking down from wear and tear) and they fit in your wallet. I carry this with me at all times. I had the same problem you did, the "should I? Shouldn't I?" dilemma as comes to taking a condom with me. I always struggled about that, so this fixes the problem. I always have one, so I don't have to worry about it. This way, I almost put it out of my mind until I'm in a bathroom stall with some girl I met 3 hours, 3 shots, 2 beers, 3 long island iced teas ago.
Put one of these in your wallet WAY before seeing her again, you will forget about it and as long as you don't dump everything in your wallet on the table, she won't ever know you have one... until you are sliding one on and giving her the stiff one eye.
As coming from someone that had podling scares and the always fun wait in line at the local health dept to find out if your dick is going to rot off or not; it's worth it to be over-safe.