I'm such a dyed-in-the-wool menu user that I often ignore the very useful icons on the Standard toolbar in OpenOffice.org. This is the toolbar, usually at the top of your work area; click the picture here to see it fullsize.
Some of these icons are only in Writer, or only in Calc. See the end of this post for what to do to add icons that you don't see but think should be available.
Mail Merge (the simple one) - You can get to it without adding it to your menu, by clicking this icon.
Then this window appears, and you can go on from there. (In the next window, choose to use an existing data source.)
Pasting - The Paste icon is fine but you can click and hold down on it, and get extra options which are nice when pasting between different applications, or when you want the pasted content to be linked to the original. The options vary depending on what and where you copied, and where you're pasting.
Page Preview - You can choose File > Page Preview too, but this is quicker.
Data Sources - Click the Data Sources icon instead of choosing View > Data Sources. Then you'll see your actual data sources, as you'd expect.
Zoom - Click Zoom to see a bigger version of your document (or a smaller version).
Show Draw Functions - You can choose View > Toolbars > Drawing, but this is a lot quicker.
Sort Ascending, and Sort Descending - Select cells in your spreadsheet and use these icons to sort quickly.
Navigator - Click this icon to see the Navigator, a very useful tool for seeing what's in your document, and going to different parts of it. It's most effective with larger documents.
Here's the navigator.
New Document From Template - This is much quicker than choosing File > New > Documents and templates.
New Document - This is a little easier than choosing File > New. Click and hold down on the icon to get the choices.
Table - Just click and hold down on this icon and choose the dimensions of your table.
Show Nonprinting Characters - To show things like carriage returns and tab marks, click this icon.
Here's what they look like, showing (they don't print).
If You Don't See All These Icons (Like the New Document From Template Icon)
Click and hold down on the downward-pointing black triangle on the standard toolbar.
Then choose Visible buttons.
Then find anything without a checkmark next to it, and select it to add it to your toolbar.
To make sure you have room for all the icons, select anything with a checkmark that you don't want, and hide it.