Few tips that I still remember:
Put loads of sugar in the ice cream and it encourages them to buy more I think, something like that.
Put loads of salt in fries and then stick a coke place nearby and they'll be thirsty and desperate for drinks.
With Duck Hunt: Set the price to enter at maximum (998 I think it is), then set the prize to the cheapest prize possible (think it's 400) then set the probability of winning to maximum too. You'll be making a fair bit that way.
The code for cheating is cut and pasted as follows:
Enter the nickname HORZA on the personal info screen. This gives you several options in the game, press the following keys to activate the corresponding cheat:
Shift + C - Get $50,000
Alt + Z - All Rides Available
Ctrl + Z - All Shops Available
Shift + Z - All Facilities Available
It's not as satisfying as doing it properly though