Add variants of :edit and friends that can take a globbing pattern to open multiple files:

:Edit plugin/*.vim doc/*.doc
:Split ??_*.c

See :help wildcards for a overview of the globbing patterns interpreted by Vim.

Compare this to the default behaviour of :edit *.vim, which will either:

• open a file named *.vim if there are no matches;
• open the file if there is exactly one match;
• error out with E77: Too many file names if there are more than one matches.

Based on my answer here, which also lists some other solutions.

By default it'll map :Edit, :Tabedit, :Read, :Split, and :Vsplit. You can use :cabbr tabe Tabe etc. to use it automatically.

See :help globedit for the full documentation.