Agreed, a decent head torch. The LEDlenser ones are really good as you can focus the light to a narrow beam to brightly light up a small section of the frame.
I don't think I'd ever graft inside the ute though. I use the back (flat deck) as a table if I do need to graft away from home. My preference is to be sitting so I sit on either a fold-up chair or empty bee box. I am fortunate to have my cell raising yard at home so do nearly all my grafting on the dining table.
12 volt halogen light from The Warehouse, not too hot for larvae, gives visibility, light neck flexible. Plug removed. Adaption fits grafting van cigarette lighter socket. Long cord reaching to van back seat or outside in the shade for grafting. Each to their own - I'm not gone on a headlamp. This is my money earner - wouldn't be without it. Very cheap, not flash looking, but effective.
I was taught to graft using natural light but these days I use artificial light. Haven't tried a head torch but I'm sure it would work in an emergency. I like dark combs to graft from and for the last couple of years I have worn 2x magnifying glasses from the two dollar shop. Good light is certainly close to essential when it comes to grafting. My father did it up to a few years ago, just sitting on a bee box with the sun over his right shoulder. To be honest I'm not sure what he did on days when the light was no good but most of his grafting was in autumn and you don't get many bad days here at that time of year.