for a 20 oz soda in the dining room, (accounting for 1 refill), cost is $.42, retail is $1.50.
for a 32 oz soda for delivery, including cup and lid, cost is $.39, retail is $1.50
for a 2 liter for delivery, cost is $1.34, retail $2.00 (I store 2 liters a room temp, not in a cooler or merchandiser)
for dining room, fountain is expected by the customer, and therefore a must.
for delivery, while fountain works ok and is more profitable, a 2 liter is much more convenient for drivers to handle. So which ever you use, or even if you use both, depends on how much delivery vs. dining room business you do, and how important profit over speed and convenience for drivers is.
I use 2 liters almost exclusively packed in a Pizza/2 liter special, and give the 2 liter away. In the customers mind, a 2 liter has a value of $2 max, (since our grocery stores sell them for $1 - $1.25). So I basically plan my foodcosts with the intention of absorbing the $1.34 cost for each 2 liter, and getting no retail in return, but the total markup for the special is 60-65%.
bottom line…don’t ASSUME which is more profitable for you, or even copy us.
do all your math, set your food cost goal, get a plan on making that goal, and execute. best of luck.