I can only give limited advice here as everyones "casa cueva" will be different. The one thing I will say is though is that I was "Screwfix directs" favourite customer up until the last month before we left. I purchased a whole range of tools wanting to be safe in the knowledge that I had everything! Most of the cars and the caravan were weighed down with tools which as you will know are not light.
considering our cave was completely unreformed I have not used the following....most of which cost me considerable expense.
Plaine (still unwrapped)
Stanley knife (still in wrapping)
Assorted screws (most unused)
Assorted sds drill bits (most unused)
5x wood chisels (still in box)
And many other odd bits and peices...
Here is a list of some tools/equipment I found absolutley essential, some of which you may find surprising.
SDS Hammer drill - essential
Cold chisel (for channelling electrics)
Srewdrivers of all shapes and sizes
Hammer (used only occasionaly)
Club hammer (2.5lb) - essential
maglite (6 cell - allways handy)
Tile cutter (bring one with you)
Spanner set (essential)
Petrol cans x2 (1 deisel, 1 petrol)
Gerry can 25ltrs
Generator (supplied by a good friend - you know who you are! cheers mate)
Once we were here and visited the local hardware shops I came to realise that the money I had spent in the UK for both essential and non-essential tools had been a complete waste of money - but not everything...
Forget hand tools in the UK (hammers etc) as these can be purchased at a fraction of the cost. There is a whole selection of tools in Spain which you may not even recognise but each has its purpose and is designed for the job better than any UK equivilent. Electrical tools are different, large items such as grinders/saws/generators etc may be worth buying in the UK depending on your renovation requirments. Of course all this depends on basic economy, price and is it worth transporing them? It all depends on your situation, there are no rules.
Last thought: If I knew then what I know now maybe our pine table and 6 chairs would not have been sold for pennies and come with us to Spain instead.