If you're going to the store to buy wine yeast you should consider spending the extra ten bucks to get some yeast nutrient and an airlock too. Apple juice that isn't fresh from the press is usually fortified with vitamin C to inhibit fermentation, so the nutrient can help, but if you're pitching a load of yeast meant for 5 gallons of must into 1 gallon it prolly won't make that big of a difference.

Either way, it's worth making a starter too - mix half a cup/~200mls of juice and an equal amount of water with the nutrient if you got any, dissolve maybe 1/8th of a teaspoon/0.2g of sugar, add the yeast, cover it with a towel, let it sit overnight and dump it into the rest of the juice the next day.