As seen in below Bruce Armstrong's ribbon menu generator has used "&" before the letter in the text section is what gets converted for the shortcut key functionality.
So far, It does not seem to work. Maybe there is code I need to wright or activate.
<Item Text="&Reservation" PictureName="" Checked="false" Enabled="true" Tag="" Type="0" Visible="true" Clicked="ue_appbutton">