These jobs were not "professional", but they were certainly important in preparing me for professional work.

Cucumber Sales
Sold cucumbers from our garden door-to-door. 5 cents each or 25 cents for a bucket. Some people actually bought 4 cucumbers when there were at least 10 in a bucket.
Lawn Mowing
$1 for the front and $2 for the back yard.
Greeting Card Sales
12 boxes to get a telescope.
Dry Cleaners - Smith Cleaners
Turn ordinary hangers into pant hangers by putting a cardboard cover on the wire for 1 cent each.
Janitor - Corner Pharmacy
Deliver medicine, sweep, mop, empty trash, and wash windows. Lots of deliveries to retirement and nursing homes. Saw how the skills of a specific boss could make or break a business.
French Fryer - Wendy's
Mind numbing work, but we could put out any order in 18 seconds.
Grounds Keeper - University of Southern Colorado
Mow grass, chop weeds, water grass, mow grass, chop weeds, water grass, ... (you get the idea).
Dishwasher - Cow Palace Inn
Wash dishes and cut fruit and vegetables for the salad bar (whose hands could be cleaner?).
Auto Parts Sales - Montgomery Ward
The new guy always has to find "A radiator hose for a Volkswagen Bug" or "A 12 ounce can of vacuum" - those mechanics think they are funny.
Ranch Hand - Reyer Ranch
Learned what "an honest day's work" means. Chopped wood, dug post holes, herded sheep, baled wool, and hundred other things.
Dishwasher - All the King's Men Restaurant
Graveyard shift. These restaurants actually fill up at 3AM when the bars close.
Stereo Sales - Great American Sound
Watched first hand as the business dove into bankruptcy. Sold and installed car stereos, Atari video games, and Commodore 64 computers.
Hardware Sales - Sears and Roebuck
Sold tools, paint, and gardening supplies.
"Alternate Profit Center" Sales - Montgomery Ward
Managed a small convenience store inside the Automotive department. Sold gas, oil, soda, candy, etc. Always measure the underground gas tank before and after a delivery. If you don't, the gas you pay for will be in someone else's tank.
Dry Cleaners - Smith Cleaners
Pressing clothes and waiting on customers. Do you know how hot it can get in a cleaners in the summer? "Dry" cleaning means they wash clothes in a "dry" solvents (originally a petroleum product) rather than "wet" water.