Gel Sacks spawn on the underwater slopes of Mountain Island, including shallow waters near the beach.A good source of Gel Sacks used to be the Safe Shallows trench by the Aurora, but Gel Sacks there have since been removed from that location.
Occupying the same amount of space, four Gel Sacks provide +20 Food and +16 H20 and 980 Energy.
For comparison, a single Marblemelon occupies a 2×2 space and provides +12 Food and +14 H20 and 420 Energy.