Instructions
Research the history of both soda brands and the different styles of bottles each company used. Some websites -- such as antiquebottles.com/pepsi/ and antiquebottles.com/coke -- give a detailed history of the brands themselves. Both pages show the changes in Pepsi and Coke bottle styles over the years, and what to look for if starting a collection.
Determine if you are collecting for fun or for potential profit. Hobby collectors generally collect what appeals to them regardless of condition or scarcity. The for-profit collector needs to set a budget and search for items that have historical significance or cachet among those in the hobby. Among serious collectors, the 1915 "hobble-skirt" Coke bottle and the 1910 Hutchinson-style Pepsi bottle are consider the "holy grails" of collectible soda bottles.
Go online and bid at auction sites such as Ebay.com or check Craigslist.org under the collectibles section. While deals sometimes can be found on these sites, professional collectors prowl online auction sites and have driven up the market especially for vintage Coke memorabilia.