This question already has an answer here:
2GB is the recommended size of an usb stick for a live image. On my 4GB stick there is space to add some other packages which I frequently use (e.g. programs to make backups).
Is it possible to easily add such packages to the stick such that they are available on my live system? -->yes
Is it mandatory to use the persistent method for this purpose?
Is it possible to this such that those added packages on the stick will all automatically be installed when I install from this augmented live image stick?
What are the necessary steps for these tasks? -->see https://help.ubuntu.com/community/mkusb.
Edits: I already created an usb stick from the file xubuntu-18.04.1-desktop-amd64.iso using usb-creator-gtk. There are 695 objects in 1.4GB on this 4GB stick, so there should be plenty of free space.
Exploring this stick with GParted shows strange things:
- sdb1 with 4kB,
- then 5,67MB unassigned,
- then sdb2 with 2,28 MB,
- the rest is unassigned.
I don't believe that! I can boot from this stick and try out Xubuntu 18.04 but I have seen that some packages which I always need are missing on the stick and I would like to add them.
From the comments to this post I learned the keyword persitent and in the German Wiki https://wiki.ubuntuusers.de/Archiv/Live-USB_-_persistente_Installation/ I found an explanation for it (however this article is old and an archieved one, apparently from Jan. 2014, so it might be outdated for current versions of Ubuntu): On such an installation there is a second partition which is marked as something special to hold all modified settings of the live system including the files added to it. According to the cited article, this second partition is created this way:
sudo mkfs.ext2 -b 4096 -L casper-rw /dev/sdXY
where XY has to be modified such that it specifies the usb stick to be used. But before this step, some other steps have to be done as described in that article.
In the comments there is a reference to mkusb. Looking at https://help.ubuntu.com/community/mkusb#Persistent_live_systems I also found a reference to persistent usb drives.