The gas prices spike on holidays is an urban legend. Gas station prices are dictated by 2 things: The price they paid to buy it, and the prices of competing stations. Neither of these are impacted by holidays because gas companies ramp up production in the two weeks prior to big holidays. Their profit is on volume, not margin, so there is no incentive to limit supply thus raising the price.

Stations buy gas wholesale and markup a few pennies to cover the expenses of selling gas. They make money on convenience items (notice the $1.59 Mt. Dew?)

If you want to save money on gas, use GasBuddy.com. There is a Google Map mashup that shows all the gas stations in your area and their prices.

If you don't have access to gasbuddy, pick a station just off the highway or interestate, they always have the lowest prices because people are more likely to stop there to use the restroom, gas up, and buy convenience items. The more congested (more gas stations) a specific exit is, the more likely prices will be down.

In regards to using bubble bath: it's a great idea, but using basic bar soap is even cheaper.