We had one accident like this when our twins were 3 and immediately bought a portable potty. It uses heavy plastic bags, which sucks, but I'm not going through that again. It goes everywhere with us.
Yeah we have one too, which is great when you're near the car... We don't usually carry it with us though. I suppose we could, never really considered it.
In that case it would be really hard to believe a worker would hold you up. Ask for the code and they will give it to you if they need it. No one is so rigid about these things especially when you are a shift worker paid minimum wage.
When your kid is actively pooping their pants, the last thing you want to do is waste time asking for the code, but yes, most people are pretty understanding.
Anyone with kids understands this plight well.