How to save mail from stick to laptop?

In any case, I suggest that you copy the entire Thunderbird Portable folder to your laptop hard drive to begin, for simplicity, I suggest you just copy it to the root of the C:/ drive. YOu also want to backup the profile folder on your laptop for thunderbird as well, if you never specified where you wanted the profile stored, see this here: https://portableapps.com/support/thunderbird_portable#local_profile

Once you have backed up the profile, open Thunderbird on your laptop, click on the "Local Folders" account, then click on "view Settings for this account", make note of the "Local Directory", you are going to change this temporarily, but you need to know what to set it back to. You want use "browse" to point to your mail account on your thunderbird portable folder that you copied from your stick to your laptop. So you will browse to C:/ThunderbirdPortable/Data/Profile/Mail/(the name of your account). Restart thunderbird (laptop version). When the program comes back up, your inbox and other mail folders should contain the emails you want under the "Local Folders" account. Then all you need to do is move or copy them to the mail account where you want them to go. When you are done, you can just go and set the Local Folders path to its original setting and you will have all your mail.

If you are using a pop server for that account, you can always check "leave messages on the server" on all of your copies of Thunderbird/Thunderbird Portable and that will allow you do download the messages to each copy without losing them after the initial download.

also a Thunderbird extension called Smartsave. This extension allows you to back-up your Thunderbird e-mail to a directory of your choice. You could install this, create a folder in your ThunderbirdPortable folder and copy this folder over to your laptop and vice-versa. This is how I did it.