Vi has named buffers by typing "[a-z], followed by your yank/delete/etc command. Does tmux's vi copy-mode have named buffers? I'd like to copy various strings into different tmux buffers and be able to paste them individually
Yes, it does.
man tmux /^BUFFERS or the web copy:
tmux maintains a set of named paste buffers. Each buffer may be either explicitly or automatically named. Explicitly named buffers are named when created with the set-buffer or load-buffer commands, or by renam‐ ing an automatically named buffer with set-buffer -n. Automatically named buffers are given a name such as ‘buffer0001’, ‘buffer0002’ and so on. When the buffer-limit option is reached, the oldest automati‐ cally named buffer is deleted. Explicitly named buffers are not sub‐ ject to buffer-limit and may be deleted with delete-buffer command.
Buffers may be added using copy-mode or the set-buffer and load-buffer commands, and pasted into a window using the paste-buffer command. If a buffer command is used and no buffer is specified, the most recently added automatically named buffer is assumed.
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The buffer commands are as follows:
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load-buffer [-b buffer-name] path (alias: loadb) Load the contents of the specified paste buffer from path. paste-buffer [-dpr] [-b buffer-name] [-s separator] [-t target-pane] (alias: pasteb) Insert the contents of a paste buffer into the specified pane. If not specified, paste into the current one. With -d, also delete the paste buffer. When output, any linefeed (LF) char‐ acters in the paste buffer are replaced with a separator, by default carriage return (CR). A custom separator may be speci‐ fied using the -s flag. The -r flag means to do no replacement (equivalent to a separator of LF). If -p is specified, paste bracket control codes are inserted around the buffer if the application has requested bracketed paste mode.
I truncated some of the information (including other buffer commands); definitely take a look at the website above (or the man page) for how to use these tools.