Increase the font size of text in Sublime side bar

You will need to edit the .sublime-theme file to do this. Unfortunately, in Sublime Text 3 this file is contained in a zipped .sublime-package file, so you'll need to extract that first. Install the PackageResourceViewer plugin via Package Control, then hit ⌘ShiftP and type prv to bring up the PackageResourceViewer options. Select Open Resource, scroll down to Theme - Default, hit Enter, scroll down to Default.sublime-theme, and hit Enter again to open it.

Next, search for sidebar_label and modify the first one (on line 362) to look like this (it needs to be valid JSON):

{
    "class": "sidebar_label",
    "color": [0, 0, 0],
    "font.bold": false,
    "font.italic": false, // <-- add comma
    "font.size": 14 // <-- new line
    // , "shadow_color": [250, 250, 250], "shadow_offset": [0, 0]
},

Save the file, and you should see the sidebar font size change. You can change 14 to whatever size you want, depending on your personal preferences.

Thanks for this, just to add that, with sublime text 3 at least, i needed to modify the theme I use. e.g. Flatland Dark.sublime-theme