My tmux.conf.local to add/override defaults.

tmux.conf.local

# This needs to be in tmux.conf
# Should always be last to allow for overrides
# source-file ~/.tmux.conf.local

# Start numbering at 1
set -g pane-base-index 1
set -g base-index 1

## C-b is not acceptable -- Vim uses it
set-option -g prefix C-a
bind-key C-a last-window
#
#
## Highlight active window
set-window-option -g window-status-current-bg red
#
## Rather than constraining window size to the maximum size of any client 
## # connected to the *session*, constrain window size to the maximum size of any 
## # client connected to *that window*. Much more reasonable.
setw -g aggressive-resize on
#
## Allows for faster key repetition
set -s escape-time 0
#
##ability to select with mouse 
#set -g mode-mouse on
#
##https://github.com/ChrisJohnsen/tmux-MacOSX-pasteboard
## set-option -g default-command "reattach-to-user-namespace -l bash"
#
## Allow pasteboard commands such as pbcopy
# tmux-MacOSX-pasteboard was copied to this binary name
set-option -g default-command "tmuxified -l bash"
set-window-option -g automatic-rename on
#