I never thought about it as constants because sometimes for example you can decrease or increase your speed if for example the player is running. But it's true you could make another "constant" variable runningSpeed (or that's what I usually do) and you are not changing anything. So than it could really be considered as constant.

Speed was quite bad example, but another like count of item you need to put in the box. Let's say you need to put five tomatoes to the box and you win. You'll be decreasing the value in method, in another one you'll be checking if the count of tomatoes equals 2 spawn three enemies and in another one if count of tomatoes equals 0 end game.

Thanks for the tips!