ltrace - same as above, if
strace is not enough
perf trace - if you don't know the exact process to strace upfront
https://github.com/brendangregg/perf-tools - to track disk accesses or exec calls
env LD_DEBUG=all - debugging dynamic linker issues
Perhaps something that performs basic connectivity tests might be useful, too -- pinging the router, an external IP (like 18.104.22.168), and a FQDN (like google.com) would be a good quick test of both internal connectivity, external connectivity, and DNS resolver.
That's pretty much it, otherwise I have a whole lot of cli tools too. Things like git, tmux, mosh, rails.. but I guess they don't count.
Okay, ok pretty much all of them. :)
EDIT: ... curl, jq, cat, less, grep, awk, lynx, watch, parallel, xargs, head, tail, sqlite3, rsync, scp...