How to hide items in Unity's top panel?

Hit Alt+Ctlr+T to open terminal and run the respective command of any indicator you want to remove. You can also use Software Center to remove indicators, Just search for the indicator you want to remove.

• Session Indicator

  

  sudo apt-get remove indicator-session

  Or search for "indicator-session" in Software Center.

• Date & Time Indicator

  

  sudo apt-get remove indicator-datetime

  Or search for "indicator-datetime" in Software Center.

• Sound Indicator

  

  sudo apt-get remove indicator-sound

  Or search for "indicator-sound" in Software Center.

• Network Indicator

  

  sudo apt-get remove network-manager-gnome

  Or search for "network-manager-gnome" in Software Center.

• Power Indicator

  

  sudo apt-get remove indicator-power

  Or search for "indicator-power" in Software Center.

• Messages Indicator

  

  sudo apt-get remove indicator-messages

  Or search for "indicator-messages" in Software Center.

• Bluetooth Indicator

  

  sudo apt-get remove gnome-bluetooth

  Or search for "gnome-bluetooth" in Software Center.

Probably you are talking about your indicators. To remove them at terminal type:

• To remove weather indicator - sudo apt-get remove my-weather-indicator.
• To remove battery status indicator - sudo apt-get remove battery-status-indicator.
• To remove evolution indicator - sudo apt-get remove evolution-indicator
• To remove message indicator - sudo apt-get remove indicator-me indicator-messages.

...Just do that to any indicator you are willing to remove from your default panel. Do not forget to add to the indicator file name hyphen plus indicator. Restart your system for your changes to take effect.

If you want them back you can as well do the reverse, by typing at the terminal the following:

To install weather indicator - sudo apt-get install weather-indicator. Do the same with other indicators you wish to install.Restart your system for your changes to take effect.

This is a list of indicators I could find for Oneiric Ocelot(Ubuntu 11.10) :What Application Indicators are available?

I hope that is what you are looking for. Thank you.

The indicators all start with 'indicator-' you can easily find them in Software Center.

there's indicator-messages for the mail menu, indicator-me for the indicator showing your name, indicator-power for the battery (not sure about the name in Natty), indicator-sound for sound menu, indicator-datetime for thetime/date showing up, indicator-network for network connections like wireless/lan and indicator-weather for weather forecasts.