I've noticed that certain products online do not require a full bitcoin to purchase. My question is do you need to start with one full bitcoin in order to make a purchase of such items?
No, you can transfer fractions of bitcoins easily. From the Myths section of the Wiki:
One Bitcoin is divisible down to eight decimal places. There are really 2,099,999,997,690,000 (just over 2 quadrillion) maximum possible atomic units in the bitcoin system.
The value of "1 BTC" represents 100,000,000 of these. In other words, each bitcoin is divisible by up to 108.
As the value of the unit of 1 BTC grew too large to be useful for day to day transactions, people started dealing in smaller units, such as milli-bitcoins (mBTC) or micro-bitcoins (μBTC).