This is an obvious one, eh? Yep, crates contain all manner of goodies, including cash, and more rare units.
You can get crates numerous ways, and one of the most reliable has to be playing PVP matches.
Here you'll get crates for hitting certain milestones, and those milestones will have you at times getting guaranteed epic units or even better than that, making it worthwhile to keep playing and earning.
You will earn fuel cans as you play, and these are always worth investing in a new convoy delivery.
A single fuel can will earn you a fresh crate, only you have to wait like six hours to get it. Yikes. A second fuel can will speed this up though, and it's well worth speeding it up.
After that you're still waiting though, and it'll ask for diamonds to speed it up further. Yeah, not sure if that's worth it. You'll get a variety of crates of different rarities by doing this though, so it's definitely worth keeping up with.
Going into the shop isn't all bad. Yes, there's a lot of stuff there begging for you to invest your cash, but you can also get good stuff for free.
Hop over to the crates section daily to get a free crates. Yes, a whole free crate. And it'll be worth it.
Whether it's gold, entirely new units or just more cards to upgrade your existing units, there's never a good reason to say no to a free crate.
Now this is the section of the shop that you can't be getting stuff for free from, but it can certainly help out.
If you pop into this section you can see what cards there are available, and of course, there's a chance for you to buy some brand new units for battle.
Even if that's not what you find here, you can buy the essential cards you need to get your favourite unit promoted. Well, maybe. I mean, it depends what they have in stock, so it's worth taking a daily look.