Symbol Organizer by Jason Burns has already become a staple Sketch Plugin for many. The new option to Gather Symbols from other pages (along with some improvements to existing features) makes it even more awesome.

“Organize your symbols page alphabetically (including layer list) and into groupings determined by your symbol names. Also provides the ability to choose the granularity of the groups, reverse the layer list sort direction, layout symbols horizontally or vertically, set a maximum of symbols per row/column, gather symbols from other pages, and to remove any unused symbols (will ignore nested symbols, symbols with nested symbols, symbols used as overrides, or symbols that reside on pages other than the Symbols page)…”

Symbol Organizer Plugin example