I have done this also.
But I used a tupperware for a makeshift potty and a small carrier bag.
The people next to us had a huge catapult and were flinging all sorts of shit about all weekend and I was very tempted to ask if I could fling my bag of poo but my boyfriend at the time stopped me, the fucking bore.
Same boyfriend was also in the car with me whilst I shat myself driving us home after eating a dodgy croque madame at Cafe Rouge. Wouldn’t have been too much of an issue if he could drive so I had to continue the journey crying hysterically and my knickers full of shit.