I always use uBlock
This improves your privacy protection. Note that some ads are only not shown, but still running in background (thus they still can get some info about you such as IP).
Ad blocking also makes you more secure from malware - for example, ad blocking protects you from some malwertising, which is a major infection vector nowadays. This could also be used as argument for blocking in some "ad blocking ethics" disputes.
I usually use Self-Destructing Cookies to delete residual cookies from
YouTube, Amazon, etc. after I log out.
I suggest also to clear your ALL browser cookies once a month or so. If you don't clear all of them, they can still keep tracking you using a cookie from a third party website under their control.
And of course don't forget to log out of services like Google if you don't want all your searches to be
I use HTTPS Everywhere to protect against eavesdropping on public
Helps a bit (only if the web site actually supports HTTPS)
Flash is disabled whenever it is not in use
Good for security as well as privacy.
If I'm looking something up quickly on a public computer, I use
private browsing mode so that form entries are not logged.
Doesn't affect your privacy in general, as you have a single browsing session and could be tracked within it. Ironically, using public computer and NOT clearing your cookies could improve your privacy (by poisoning Google and other profiles), but of course comes with obvious security risks.
Note that there are many other risks using a public computer, such as installed malware or keylogger (including hardware keylogger).
I carry a USB stick that has a portable version of Firefox with the above
This is a bit helpful, but again the main issue with public computer is (lack of) security, and possibility to have keyloggers, from which your portable firefox won't protect.
I am aware that Google, Facebook, etc. track my activity regardless of
what I do on my local system.
However your actions make it harder for them. If you do google search while logging in, they KNOW it is you. If only your IP matches, it might or might not be you, so the profiling degree is less confident.
And regarding Google, make it a habit to spend 15 minutes a week to "poison" your profile, by searching for something you would never search or never be interested in, and by sending out emails in Gmail (to your other or non-existent accounts) using topics/keywords as far away from your interests as possible.