You don't need and won't get the V5 for a hire car from any company.

Instead you will get a VE103 Vehicle On Hire Certificate IF the hire company agree to let you take the car across borders.

As Tabetha says, different countries have different rules on equipment to be carried, like bulbs, hi-vis for driver only/all passengers, triangles, etc. (eg, if you need specs to drive, Spain insist that you carry a spare pair in the car).

The responsibility for all this is yours, though our hire car in Spain last year did have a single hi-vis jacket.