The following applications from below are in my list of Startup. Which one of them are strict necessary for the system? How can I remove those not necessary from Startup (but not from my laptop)?
AT-SPI D-BUS BUS
Backup Monitor
Bluetooth Manager
Certificate and Key Storage Gnome Keyring: PKCS#11 Component
Chat Telepathy indicator service
Check for new hardware drivers Notify about new hardware drivers ...
Desktop Sharing Gnome Desktop sharing server
Disk Notifications Provides notifications related to disks
Files
Gnome Settings Daemon
GPG Password Agent Gnome Keyring: GPG Agent
GSettings Data Conversion Migrates user settings from Gconf to dconf
Gwibber Update your microblog and view others' statuses
Mount Helper
Network
Onboard
Orca screen reader
Personal File Sharing
PolicyKit Authentication Agent
PulseAudio Sound system
Screensaver
Secret Storage Service
SSH Key Agent
Ubuntu One
Update Notifier
User folders update
Zeitgeist DdataHub
Thanks, J.