If you want to do it for long periods of time (Not 24 hr by the way).

Then treat it like a day at work.

Get up, eat a complex carb breakfast, shower. (all the time planning the strategy)

Play the game for 1.5 hours. Go and exercise for an hour. Play for 1.5 hours. Have lunch for an hour. Play 1.5 hours. Have a half hour coffee break. Play again for an hour or two.

By the PC keep trail rations, fruit (banana or something not to juicy), water.

It is far better to break up the play as much as possible. You can still plan strategy away from the PC (you might even dream about it). But continous play will only dull your reactions and enjoyment.

It is better to play it for 40 hours in a week like a job and at the weekend still feel fresh and fine.