Spain really is no different to any other European country, in that you are very unlikely to be stopped in any kind of spot check for anything.
As you are on holiday, away from the UK, take with you the originals documents listed above. By all means store copies on your phone or iPad or away in the cloud. Why take the originals? Should you lose them (really, how likely is that) it’s a lot easier for you to explain to someone in the UK that you’d like a fresh V5 or driving licence, than to some rural policeman in the sun (or pouring rain) that you are carrying only a crumpled copy (made on some shonky ink jet printer from Lidl) or while you try to summon up the cloud with no phone signal.
A fluo jacket / tabard. Again, you’ll very probably not need it and you might, in any case, already ride in one anyway. Why? Having having had to mess about in the falling light on a dangerous bend in Luxembourg, summoning an ambulance to help a rider and pillion who had carried on into the barrier, you are very pleased to be as visible as possible to other vehicles.
Headsets / intercoms? Nobody is going to stop and check you. Unless that is you have committed a crime so heinous, that using a headset is the least of your worries.
As to spare bulbs *, tins of sticking plasters, distress beacons, maps of Poland, an entire apothecary’s, eight pairs of trousers, a tartan flask of brew and letters of introduction from your mum? No, unless you feel you really must.
* Good luck replacing the LED light system on the side if the road, without at least a Swiss Army knife and probably more.
Oh yeah, my phone so I can take photo`s.
