There are a lot of threads giving advice into methods to get more SG. One of those (and possibly the most easier and profitable one) is to use the App-Zone, on the GameHag mobile app. You can get up to 100 SG every 24 hours.
You can also do tasks and contracts, but if you have any difficulty with those, the App-Zone is your best bet!
@m4nac0lypse sadly the weekly crate only offers runes, so I'd say that's not a good idea