なにはともあれ Package Control のインストール

cd ~/Library/Application\ Support/Sublime\ Text\ 3/Packages/
git clone https://github.com/wbond/sublime_package_control.git "Package Control"
git checkout -b python3 origin/python3

ST3 を再起動。問題なく動いた

ほかのパッケージ

SourceTree.app Menu

reloading plugin SourceTree.app Menu.SourcetreeCommand
Traceback (most recent call last):
  File "/Applications/Sublime Text.app/Contents/MacOS/sublime_plugin.py", line 72, in reload_plugin
    m = importlib.import_module(modulename)
  File "X/importlib/__init__.py", line 88, in import_module
  File "<frozen importlib._bootstrap>", line 1577, in _gcd_import
  File "<frozen importlib._bootstrap>", line 1558, in _find_and_load
  File "<frozen importlib._bootstrap>", line 1505, in _find_and_load_unlocked
  File "<frozen importlib._bootstrap>", line 313, in _call_with_frames_removed
  File "<frozen importlib._bootstrap>", line 1577, in _gcd_import
  File "<frozen importlib._bootstrap>", line 1558, in _find_and_load
  File "<frozen importlib._bootstrap>", line 1505, in _find_and_load_unlocked
  File "<frozen importlib._bootstrap>", line 313, in _call_with_frames_removed
  File "<frozen importlib._bootstrap>", line 1577, in _gcd_import
  File "<frozen importlib._bootstrap>", line 1558, in _find_and_load
  File "<frozen importlib._bootstrap>", line 1522, in _find_and_load_unlocked
ImportError: No module named 'SourceTree'

ここで止まる。モジュール名がだめっぽい。
SourceTree パッケージを使う事にした。こっちは動く。

SublimeClang

Package Control 経由だとダメ。github の master brach の HEAD もダメ。