How to pipe multiple commands into a single command in the shell? (sh, bash, ...)

How can I pipe the stdout of multiple commands to a single command?

Example 1: combine and sort the output of all three echo commands:

echo zzz; echo aaa; echo kkk

desired output:

aaa
kkk
zzz

Example 2: rewrite the following so that all the commands are in a single command-line using pipes, without redirects to a temp file:

setopt > /tmp/foo; unsetopt >> /tmp/foo; set >> /tmp/foo; sort /tmp/foo