Open the box, unpack stuff, got upset that the power supply has a new MagSafe adapter - this means my old power brick will not serve without an adapter.
Charge the battery. Set up the basics and register the Mac.
Log in for the first time. Change the background, make the dock smaller.
Set the trackpad to the tap mode - I prefer light tapping to strong clicking.
Remove some apps from the dock that I rarely use: the stock email reader, FaceTime, Contacts, etc. Many of these are integrated in Google apps.

Tweaks

Fix Safari (and Chrome) settings to not save passwords, and start with my favorite start page.
Move Terminal shortcut to the Dock
Terminal->Preferences->Settings->Shell-> change "When the shell exits:" to "Close if the shell exited cleanly"
Terminal->Preferences->Settings->Window change width to 120 - I wan to see long messages.
System Preferences -> Languages and Text; also in Keyboard, and add and enable options for Latvian text input support.
System Preferences -> Keyboard -> Shortcuts -> Full Keyboard Access: in windows and dialogs... [x] all controls

AppStore

Install some apps from the AppStore:

TextWrangler - the text editor
Evernote - take notes, save in cloud
Numbers, Pages, Keynote - Apple office
MplayerX - play videos nicely
SmartConverter Pro - convert most any video formats to common target formats
The Unarchiver - easy zip file management
Caffeine - Turn off screen saver
Sketchbook Express - drawing program by AutoCad
Kindle - read books from Amazon
Xcode - for development and command line tools
- Xcode->Preferences->Downloads-> install Command Line Tools

Install some apps from other sources, or directly from the developer.

Google Chrome
KeyRemap4MacBook - to rearrange the keyboard. Here are some of my favorite mappings:
- Control+Arrow to Option_L+Arrow, to get the control to skip words, not desks.
- Command_R to Option_R, or else I keep pressing command+a to get 'ā' for my Latvian text, but it selects everything instead, and kills the text with the next stroke.
- Option_R to Forward-Delete, to get my Del key back and close.
- Z+X to Left click (to make drag and drop easier with the touch pad)

There are a few things I am not sure will stay long term, but anyway, there they are:

nginx - webserver for development needs. Yes, Mountain Lion still has Apache somewhere within, although the enabling checkbox has been removed from the system settings. So, I will try the nginx.
node.js - for some experiments.

There are some things that I have decided to stay away based on previous experiences or storage and other restrictions.