When you visit certain cities, special options are given to you. 

Anaheim / Santa Ana / Garden Grove There is an amusement park here - If you 
allow your men to have a go on the rides, morale is improved. 

Dallas / Fort Worth Here you can get some fuel addatives. 

Detroit Huge power-ups for your vehicles. 

Houston The space research centre is here! You can get some food additives 
here. 

Las Vegas You can allow your men to gamble. I'm not sure what this does, 
though! 

Minneapolis / St. Paul The home of the Mayo Clinic. You can get a doctor here. 

Napa / Vallejo / Fairfield Wine country! If you allow your men to indulge some 
wander off in a state of drunkeness. Lose some men! 

New Orleans The Mardi Gras is in town! If you allow your men to join in with 
the celebrations morale is improved. 

New York The home of the U.N. - get a politician. 

Pittsburgh Huge power-ups for your vehicles. 

San Jose / Mtn. View You can visit SSI headquarters! Here your game will be 
altered by an SSI official and you will gain many things (Power ups for your 
vehicles, doctor, politician, drill sergeant.) 

NOTE: These may not be all of the special cities, though. Explore and find out.