To add to fooot's answer, emergency equipment required on aircraft varies based on the routes the aircraft will take.
In the most extreme case, if the aircraft will be performing Extended Over-water Operations (EOW), then it requires rafts, life vests, and more:
14 CFR § 121.339 - Emergency equipment for extended over-water operations.
a. Except [... ] no person may operate an airplane in extended overwater operations without having on the airplane the following equipment:
A life preserver equipped with an approved survivor locator light, for each occupant of the airplane. -- that's a life vest
Enough life rafts (each equipped with an approved survivor locator light) of a rated capacity and buoyancy to accommodate the occupants of the airplane. Unless excess rafts of enough capacity are provided, the buoyancy and seating capacity beyond the rated capacity of the rafts must accommodate all occupants of the airplane in the event of a loss of one raft of the largest rated capacity.
At least one pyrotechnic signaling device for each life raft.
An approved survival type emergency locator transmitter. [...]
c. A survival kit, appropriately equipped for the route to be flown, must be attached to each required life raft.
If the aircraft will go over water, but to for "extended over-water operations", then the requirements are lighter:
14 CFR § 121.340 - Emergency flotation means.
(a) Except as provided in paragraph (b) of this section, no person may operate an airplane in any overwater operation unless it is equipped with life preservers in accordance with § 121.339(a)(1) or with an approved flotation means for each occupant. This means must be within easy reach of each seated occupant and must be readily removable from the airplane.
And if it does not go over water at all, or very very shallow water only:
(b) Upon application by the air carrier or commercial operator, the Administrator may approve the operation of an airplane over water without the life preservers or flotation means required by paragraph (a) of this section, if the air carrier or commercial operator shows that the water over which the airplane is to be operated is not of such size and depth that life preservers or flotation means would be required for the survival of its occupants in the event the flight terminates in that water.
Depending on the airline and its routes, they may have all their aircraft equipped for EOW anyway (added cost but more flexibility), or only part of them for EOW and the rest for other overwater operations, or only the latter.
Extended overwater operations are defined as:
with respect to aircraft other than helicopters, an operation over water at a horizontal distance of more than 50 NM from the nearest shoreline.