I don't deal well with anything unexpected. I think the best way to explain it is feeling lost, and helpless. If I lose something, I panic because I'm never sure where to start looking, or how to go about it. The last time I lost my keys, I cancelled everything I had to do that day, cried for a while, and then, while still crying, started looking for my keys.
I don't often lose things because I've gotten very systematic about what I do when I leave, where I keep my keys when I'm out, and what I do when I come home. Similarly, I used to lose my glasses all the time, but I rarely do now because I only put them in one designated spot in each room.
If something unexpected happens during my day, I get very upset about that. If part of my day requires travelling, I leave at least an extra half hour so that if I get lost, or if something comes up, I have time to calm down, figure out what to do, and then do it.
I do impose regularity in my life because otherwise I'm a wreck. I get very scattered, and I become unsure of what I have done, what I haven't done, and what I should do next. My significant other does his best to accommodate that need for regularity (letting me know what he would like to do ahead of time, not interrupting when I'm getting ready to go out etc.), and I do my best to remain as flexible as possible, or at least to stay calm when something comes up so that I'm able to deal with it.