My husband works for an oilfield service in Calif. He is on call and sometimes when he goes to work he is gone for 14-16 hrs. While on location he sometimes waits in his truck for the job to start and other times he continuously works for hours at a time. He is by himself and has no one to relieve him for breaks or lunch. He does however is able to eat his lunch quickly and get back to work. He is paid for this time. Shouldn't his employer provide an actual break or lunch period?

Generally speaking, yes, but there are some exceptions. See here:
http://www.dir.ca.gov/dlse/FAQ_MealPeriods.htm

There may also be exceptions under some Industrial Wage Orders (separate from the California Labor Code). Hopefully, our employment law guru in California will be along shortly.

What exactly does he do?

From the applicable Wage Order:
(D) Unless the employee is relieved of all duty during a 30 minute meal period, the meal period shall be considered an "on duty" meal period and counted as time worked. An "on duty" meal period shall be permitted only when the nature of the work prevents employee from being relieved of all duty and when by written agreement between the parties an on-the-job paid meal period is agreed to and complies with Labor Code Section 512.

Given that you state that he works alone and does not really have time to take a break and that he is paid for the break, if they have a written agreement as to this arrangement , then it is legal.