Spent most of my London life queuing for theatre tickets as for me it was the only way to get in. Spent hours in the Royal Opera House queues for gallery tickets. The first tube train, the 5.10 from Canon's Park, the smell of oranges and urine as you hit Covent Garden station, the ladies of the night and the porters urinating over the vegetables and the joy of getting the precious tickets for wonderful first nights. Never had any luck with the Gala's though although I did get to one by being in the ballet there!
Later I found the Standing tickets. By law the theatre has to reserve tickets for daily sale and these could be bought on the day at around 4pm. These were cheap and allowed you to stand at the back of the stalls Stood through The Ring this way at 16!
Obviously The Proms, queuing for these concerts was great fun when a student. Sold out musicals could be seen too.
Turning up in the foyer one can usually get a ticket from someone who has one to give away. Royal Festival Hall and Wimbledon Center Court are good places for this.
When I married my GP Opera loving husband I still had to queue although this time for the posh part. However I still preferred the gallery for ballet!
Now when I come to London I still do the same but I spend more to sit. I would still stand if the performance was one not to miss.