Assuming that:

It is the only beverage available,

it is not particular hot where you're serving it,

people are not eating anything dry, salty and/or spicy,

I'll say that each person will on average drink 2 glasses per hour.

If you have tall glasses they should be around 250mL each, so you'll have a consumption of 25 2 Liter Sodas per hour.

If you provide Ice you can save 1/3 of the soda and average will probably only increase to 2.5 glasses per hour. So that leaves you at around 21 2 Liter Sodas per hour

It is the only beverage available,

it is not particular hot where you're serving it,

people are not eating anything dry, salty and/or spicy,

I'll say that each person will on average drink 2 glasses per hour.

If you have tall glasses they should be around 250mL each, so you'll have a consumption of 25 2 Liter Sodas per hour.

If you provide Ice you can save 1/3 of the soda and average will probably only increase to 2.5 glasses per hour. So that leaves you at around 21 2 Liter Sodas per hour