Can anyone ID these two books?

1… A bunch of teens survive some kind of disaster and go see if they can find survivors. A chilling scene I recall had them finding a dead person who had fungus/mold growing on him.

2.Took place sometime in the 1920s-50s and had a boy going on adventures with an older female relative. At one point they show up at his parent’s house with a muskox or yak named Muscatel.

The first I checked out from the YA section in the early '00s and the second I read at a relatives in the same time period.

A quick search found the second.
Around the World With Auntie Mame
By Patrick Dennis

That’s one of them, thank you!

If no one here comes up with an answer for the first one, I suggest going to Goodreads and asking in their Name that Book section. They’ve helped me locate several books I read as a teen and wanted to reread.

What’s the Name of that Book??

Here’s a list of post-apocalyptic teen fiction that might be a place to start looking for #1.