I was in early labour with ds for 4.5 days, followed by 12 hours of active labour. Contractions ranging from every 5 minutes, to an hour apart for nearly 5 days and nights. My advice is sleep as much as you can. You might not feel hungry but keep drinking water, and make sure you are emptying your bladder frequently. Things that worked for me were warm baths, paracetamol, sitting facing the back of a dining chair, with a pillow between me and the back of the chair (I even slept like that!). And watching a timer during contractions, or counting. I knew it wouldn't last longer than about a minute each time so once each contraction got to 30 seconds I knew it was almost over. Breathing, and remembering not to tense as much as possible. The tens machine did nothing for me. Pethedine was amazing, but it did knock me out. I had a fantastic epidural in the end with my first and it was the best decision.
My other advice is be flexible and open to what might happen, dont be too wedded to your birth plan. With my second I foolishly assumed I would have a similar labour, long drawn out and exhausting, and planned to have an epidural again. In reality I had about 3 hours of active labour and delivered on gas and air alone, no time for an epidural. It took me a moment to get my head around the fact I wasnt getting an epidural and it very nearly sent me into a panic. Gas and air is fab, though, it doesn't remove the pain, it just stops you caring about it, and once you stop breathing it in, you come back to normal very quickly.
Finally the thing that helped most of all, other than amazing midwives both times, was DH. He was calm, supportive, encouraging, and protective of me when I needed it. He managed all the messages from family, kept everything else going in the house while I laboured, and was just amazing. So my other advice is choose your birthing partner carefully, and make sure they know what your wishes are.