On many flights, I was told that a life jacket is under my seat and safety card is in the pocket in front. Is there any regulation that ensures that life jackets and safety cards are on-board on all flights?
The FAA has a similar requirement (commercially under part 121)
(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.
(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.
In other words they are only actually required (per FAA regulations) when operating over water so not every plane (route provided) technically needs them. However many airplane seat bottoms may double as a personal flotation device so many planes are equipped with them by the nature of their construction.
The UK Air Navigation Order contains specific requirements in Appendix 10, based on ICAO recommendations. You won't have to look very far to find similar requirements specified by the regulatory authorities in any major country.
18.104.22.168 Single-engined aeroplanes.
Recommendation . - All single-engined landplanes when flying en route over water beyond gliding distance from the shore should carry one life jacket or equivalent individual floatation device for each person on board, stowed in a position easily accessible from the seat or berth of the person for whose use it is provided.
6.3.3 All aeroplanes when operated on extended flights over water shall be equipped with:
a) when the aeroplane may be over water at a distance of more than 93 km (50 NM) away from land suitable for making an emergency landing: 1) one life jacket or equivalent individual floatation device for each person on board, stowed in a position easily accessible from the seat or berth of the person for whose use it is provided;
b) when over water away from land suitable for making an emergency landing at a distance of more than 185 km (100 NM), in the case of single-engined aeroplanes, and more than 370 km (200 NM), in the case of multi-engined aeroplanes capable of continuing flight with one engine inoperative: 1) life-saving rafts in sufficient numbers to carry all persons on board, stowed so as to facilitate their ready use in emergency, provided with such life-saving equipment including means of sustaining life as is appropriate to the flight to be undertaken; and 2) equipment for making the pyrotechnical distress signals described in Annex 2.
User11933, has reproduce the legislation refering to those specific items.To answer your other question ie:who checks it.The flight attends do, in theory. After each flight they are supposed to check and make sure none is missing.It is part of the equipment of the aircraft and as such, listed in the MEL.(Minimum equipment list) which is the document listing all the systems and equipment mandadory on board. Obviously the captain is ultimately responsible. On smaller aircrafts with no FA, it is actually up to him or to the FO by delegation, to make sure they are on board before departure. Hope that clears it up :-)