Wow, my battery died yesterday too, but it was under warranty so I got a free replacement. Luckily, I also had a portable power booster/compressor (Campbell Hausfeld Power Pal) to get me up and running long enough to get to Wally World. I've used mine on several occasions.

I usually keep about $30 in singles in my car for emergencies, and $10 in the bag on my mountain bike. If I need more $$, I pull out the plastic.