I found this cool app last week and it works tremendously well if you are unable to connect to the internet and want to play skirmishes with the AI. It's particularly useful for when you're travelling. I played some skirmishes on my laptop while going to the cottage last Friday and while coming back on Monday.
The features are quite elaborate, matching the options of the in-game skirmish set-up, but adding additional features, such as the ability to load Custom AI, fuck around with cheats, and even play custom maps. All of this is launched from the desktop application so there's no need to wade through the initial game loading.
Here's the official webpage with download links:
sc2ALLin1 (v10.3.3) (Offline StarCraft 2 RETAIL Launcher)
Now they just have to come out with a good LAN emulator. I saw a video of one on youtube which appears to work, but the damn download requires a survey to be filled out which is always bullshit.