When you wrench on a Subaru as long as I have, you can just look at the bolt and immediately know whether it's an 8, 10, 12, 14, 17, 18, etc.
If they're fastener bolts, 8, 10, 12, 14 are going to be your standard. When it comes to things that I change often (like oil drain plug), I write this with a paint marker under the hood of any car I change the oil on. I don't need to remember this with Subaru because I have it memorized, but it helps in case you ever forget. But as it's been mentioned, having a tool set with just 8, 10, 12, and 14 sockets, you can pretty much take the entire car apart except for some of the larger suspension components and a few other odd bolts.