We can refer collectively to those stratagems I suggested last time as the what's wrong? syndrome.
Other writers on Egocentric Walking Theory refer to it in terms of "What did I do with it?" and so on; but I like a title which reflects what those walking behind are thinking.
And it doesn't just apply to ticket gates. You can use it to great effect in a supermarket. Have a chat with the cashier; pack your purchases; and then behave as if it had never occurred to you before that you have to pay -- and then you can wonder where you put your cash or your card. Why not ask if you can pay partly in cash and partly by card? Only one per store, I am afraid; or they'll remember.
If they have a loyalty card, almost tender your payment and then remember the card.
I was going to say: if you are registered. But there is scope for offering an unregistered card. It won't work, of course; but think of the delays!
And as you leave the ticket gate, use What's wrong? as much as you can -- stay within the gate exit so that others collide with you, stand in the main thoroughfare, checking your pockets etc.
Similarly, in the supermarket, stay in the narrow payment aisle while you adjust things in your trolley; leave the aisle a bit but not enough; put your trolley across the main aisle out of the supermarket.
For your homework, think of as many venues where you can apply What's wrong?