From Wikipedia:
3Com — Network technology producer; the three coms are computer, communication, and compatibility.
A&W Root Beer — named after founders Roy Allen and Frank Wright
Coca-Cola — derived from the coca leaves and kola nuts used as flavoring. Coca-Cola creator John S. Pemberton changed the ‘K’ of kola to ‘C’ to make the name look better.
Pepsi — named from the digestive enzyme pepsin.