Theatrical marathons can either be heaven or absolute hell

Wagner's Tristan and Isolde will always smell of kebabs for me. That's because the first time I actually went to see it in a theatre – in Cardiff – I spent the long interval in a kebab shop. That's the kind of girl I was.

That was also, as far as I can remember, my first theatrical marathon, the first moment I committed to spending a day watching long-form culture. I remember Abel Gance's restored Napoleon at the Birmingham Hippodrome too – though mainly because the theatre was so hot in the gods that I thought I might pass out during its five and a half hour running time.

To get a long-stint in the theatre right, you need to be ready for all emergencies

From that experience I learnt the key to a long-stint in a theatre is getting the essentials right. You need to be ready for all emergencies; you certainly need to know where you are going to eat and what you are going to drink. (Alcohol can be a disaster in these circumstances.) I think that is part of the joy of the entire event. You need to plan as if for a marathon run: the right clothing, comfy shoes. And the added pleasure, of course, is that you don't actually have to move apart from a few well-judged stretches in the intervals.

My friend Bill is my chosen partner in these epic undertakings. We share an obsession with theatre and a willingness to sit in the dark for hours in search of cultural enlightenment. Sometimes the experience is actually revelatory: my favourite was the RSC Histories Cycle in 2008, directed by Michael Boyd. Over more than three days we vanished into the theatre every morning, and emerged blinking late every night, losing ourselves in an absolutely towering production of every one of Shakespeare's history plays, in chronological order of kings. It was unforgettable. You saw the same people every day, off-stage and on, and your mind was full of a world where the great debates about order and monarchy, about the nature of society, about good and evil, sprang to such vivid life that they were more important than the news around us.

It's hard to match that, but I also remember with great pleasure Rona Munro's triumphant trilogy of The James Plays at the Edinburgh Festival and Alan Ayckbourn's The Norman Conquests at the Old Vic.

The longer a theatrical marathon feels, the less good the play

The general rule of thumb is that the longer a theatrical marathon feels, the less good the play. I struggled a bit with the hardness of the benches at Shakespeare's Globe at the end of Hamlet yesterday but I know that was because I was dismayed at the production. The performances, though genial, just didn't offer enough to chew on over a day that had also embraced the same actors in As You Like It in the morning. This kind of pairing is sometimes inspiring; it makes the plays talk to each other. Yesterday, the conversation fell apart.

Equally, in my other marathon of the past fortnight, I found The Inheritance at the Young Vic last Saturday (excellent Turkish meze in the long interval) a mixed delight. I was overwhelmed with admiration for Stephen Daldry's direction and the all-round brilliance of the acting, but I did spend a fair bit of time imagining how I could cut down Matthew Lopez's text to a more manageable length than its current seven hours. On the other hand, I sat through Angels in America in Marianne Elliott's production at the National Theatre while in the middle of chemotherapy; I may have needed a lie down in the long break, but I didn't wish a single line or a single second of that wonderful pair of plays away.

Tony Kushner seems to me to be a bit of a Wagnerian playwright, when I come to think of it. What you need to sustain you through a lengthy theatrical odyssey is intellectual richness. Even more than a kebab.