"HELP! I can't find ___________ in my invoice/estimate admin..."
Check out the "screen options" tab at the top-right of your invoice/estimate admin.
Once you click that, you can check and un-check any options that you want to be shown in your invoice/estimate admin. You can also check-out the nifty "layout" feature and decide if you want your invoice/estimate admin displayed in one or two columns. Save some scrolling and go for two columns!