O/S
/tmp as tmpfs - https://wiki.archlinux.org/title/tmpfs
logs that don't go on forever - https://github.com/azlux/log2ram
systemd logs that don't go on forever /etc/systemd/journald.conf:
SystemMaxUse=50M
Faster, more responsive kernel (if stuck on an LTS for everything else) : https://liquorix.net/#install
Ubuntu Specifics
Get rid of 'advantage' and ESM Spam https://vi-server.org/pub/fake-ubuntu-advantage-tools.deb (via https://askubuntu.com/a/1438510/1681137)
zswap - add zswap.enabled=1 to GRUB_CMDLINE_LINUX_DEFAULT in /etc/default/grub
zram (faster, in memory swap to be used in preference to real swap) - https://askubuntu.com/questions/174579/how-do-i-use-zram
Much smaller kernel images in /boot - set COMPRESS=xz in /etc/initramfs-tools/initramfs.conf (per https://askubuntu.com/a/1429218/1681137)
Reduce Snap disk space usage by >30% : sudo snap set system refresh.retain=2 (https://superuser.com/questions/1310825/how-to-remove-old-version-of-installed-snaps)
Save almost two further gig by adding to root's crontab : 8 19 * * * rm -rf /var/lib/snapd/cache/*
If you set the timeout in /etc/default/grub, also add GRUB_RECORDFAIL_TIMEOUT=$GRUB_TIMEOUT or it won't work on EFI systems ( https://bugs.launchpad.net/ubuntu/+source/grub2/+bug/1800722/comments/13 )
Apps
Work around Snap's not being able to see /tmp : https://askubuntu.com/questions/1263843/how-to-allow-snap-applications-to-access-tmp-folder
WireGuard VPN
Don't try and use KDE's GUI, the connection will either delete itself with an error, or not work.
Run nmcli connection import type wireguard file ~/Documents/wireguard-home.conf (this is the same file that works with wg-quick up).
It'll then appear and work fine, and you can set hotel WiFi connections to always use it etc as normal.
You can confirm and monitor with sudo wg.
FireFox
MultiRow tabs : https://github.com/onemen/TabMixPlus#installation
Tabs that look like tabs : https://www.userchrome.org/firefox-89-styling-proton-ui.html#tabstyler
LibreOffice
Add updated LibreOffice PPA : https://launchpad.net/~libreoffice/+archive/ubuntu/ppa
GIMP
As a flatpack to get the good plugins working like content aware fill ('heal selection') : https://github.com/bootchk/resynthesizer/wiki/Install-Resynthesizer#flatpak
DotNet Apps fail with `Couldn't find a valid ICU package`
Add Environment=DOTNET_SYSTEM_GLOBALIZATION_INVARIANT=1 to [Service] block of SystemD unit e.g. sudo systemctl edit awsvpnclient.service and/or set the same on the menu item