Caliber, the indicator at the top show the food, metal, gold and so on like you said. When you hold your mouse above each resource it shows the rate per turn. I use CTRL + M to give me 1000 of each of the standard resource and when I hold my mouse above say crystal it say I have 1000 in stock at a rate of 0.0 per turn. Funny, there no codes for food or the other harder to get stuff.
The game treats food differently than other resources. You can never stockpile past the number you are earning it by. This number is derived by adding all the food production from any cities that are producing and then subtracting any cities that are showing a negative value for food. IOW every city will show either a plus or minus for food "output" (unless it's balanced then it won't show any number) and the number at the top of the screen reflects the total of your cities.
I'm guessing that if the trainer puts up a number at the top that doesn't correlate at all with your cities total then the game will crash when you end the turn. Again food is just treated differently and cannot normally be stockpiled.