Multiple selections in VIM

No, this is not possible without plugins.

But you can copy multiple lines into the same buffer, if that solves your problem.

• To start the ‘Accumulation Buffer’:
  • mark a section to copy in visual mode,
  • press "a to operate on the buffer a with the next command and
  • yank it as usual (y).
• To add to that buffer:
  • mark the next section and
  • press "A (capitalizing the buffer name means “do not overwrite the buffer, append to it instead”)
  • and yank again using y.
• You can then paste the accumulated buffer a at any time using "ap.