I'm not sure on power manager, but on volume you have a few options. The reasiest option is to right click anywhere on the menu bar, go to 'add/remove panel items', then go to 'panel applets' then 'add'. From there choose 'volume control'.
I have had some issues with this volume control software--my headset is not always recognized and the maximum volume is very quiet. If you have these issues or for any other reason want the same volume control that is used in Gnome, you can add that to the menu bar instead. This is by far my preference, just a bit more complicated. To do this, open the terminal and type the following commands:
After installing all three packages, right click the menu bar, go to 'add/remove panel items', go to 'panel applets', go to 'add', and select 'indicator applets'. After adding indicator applets (while still in the panel preferences box), select 'indicator applets' on the list, then click 'edit'. From there check the box that says 'sound menu'
sudo apt-get install lxpanel-indicator-applet-plugin
sudo apt-get install indicator-application-gtk2
sudo apt-get install indicator-sound-gtk2
At this point, you should have the Gnome version of volume control on the menu bar. Much nicer than the default LXDE versions.
If any of this was unclear or you want any part of it in more detail, PM me, I might not check back here but I can give a more detailed walkthrough or screenshots if necessary.