The way I would approach this is with math, because humans are bad at probabilities.
What are the odds of your stuff getting taken? One in a hundred would still be compatible with 'nothing happened the last hundred times', and one in a hundred is probably a reasonable estimate. Let's go with one in five hundred, since you're feeling lucky.
You have two thousand pounds of stuff in your bag, which would disappear if someone took it. Simply multiply to get the expected loss: 0.002*2000 = four pounds. You trip to the loo cost you four pounds. (If the odds are actually closer to one in a hundred, your trip cost you twenty pounds instead.)
If you're ok with paying four pounds to go to the loo bag-free, then hey, victory is yours.
But remember that you are playing a lottery here, and that it's a net monetary loss in the long run. If your time/effort tradeoff is worth the money then so be it, but make that decision consciously and based on data. Do not try to 'gut feel' your way around probabilities of less than one in fifty.
The OP says that she's insured, so theft of the items would be significantly less costly than £2000.
I am just working on a list of rationalist rules I live by, and this is the one I have most confidence in, so it seems a good topic for my first ever post (which will be short as I have to be on a train in 15)
Since people routinely exaggerate risk, and social norms pull us towards the crabs in a bucket effect (especially for women) I want to correct for that. (Preferably without ending up with a giant Rob Me sign over my head, but that's not the direction I err in.)
For example, there was this rationalist walked into a bar. I had a lot of luggage - everything I need for a four day break, including over two thousand pounds worth of electronic devices and binoculars. I am insured, but it would be an especially annoying time to lose stuff. I had a coffee and then I needed the bathroom, which was far away through a lot of people.
I knew logically how little risk there was in leaving all my stuff; a Highland bar in the middle of the afternoon is even safer than where I live in Edinburgh, and no-one was pinging any alarm bells, but I still spent more time than I'd like to admit convincing myself I didn't have to drag the huge bag with me to the ladies and back. Yes brain, even though I'm alone, and the customers are men, and I'm a middle aged woman, and my mother would freak if she saw me...
Of course it was fine, like it was the last hundred times. One day I hope to not even have to persuade myself, but meanwhile I notice my prediction was correct and feel just a little bit pleased with myself.