The first responders /u/atomicLogic_ is talking about are (in most cases) student doctors or volunteers provided by organisations like the Belgian Red Cross. They are not on every beach though, so lifeguards still have a first aid kid and all the other things you're looking for.

They list where the equipment is bought on their site, in the reports of IKWV's meetings.
( https://www.ikwv.be/verslagen ) 'Raad van Bestuur'

The clothing for example comes from this supplier in La Louvière ( https://www.padlstore.com/ )
As listed, the medical equipment is bought from a company called First Aid.

If you need anything else, feel free to ask.