I always get in trouble on this question as my opinion is a lot different than others. An 8 day trip is pretty long for your second trip. Not impossible, but it could easily be a mess with gear thrown together without a plan that is too heavy.

One overnight trip before an 8 day trip probably isn't enough to learn how to use the gear well. You can help yourself by simply hiking a few miles around the neighborhood with your pack and spending the night with the gear you will use in your backyard if possible, or in an apartment with the windows open as a last resort. Be sure to walk in the rain whenever possible.

The time to find out the method you use to keep your sleeping bag and extra clothes dry isn't working is at home, or at least on an overnight trip. It's better to find that cheap poncho you buy splits on the first use when you are at home. It is also helpful to be able to set up the tent in a short time without confusion.

Almost everything else is secondary to a good night's sleep in a dry tent with a good bug screen. That's a bit of an extreme opinion, but it works for me.

I've put together a list of gear for a "beginner's pack." It's also one I'd be happy to carry. You don't have to buy it all at once, and you may never buy some. But it gives you an idea of what subsitutes should look like.

Some comments. I use my backpacking clothes a LOT at home. I've pretty much given up driving except to get to a trailhead. I walk in all sorts of weather, so I'm real familiar with how to stay comfortable.

Here is my gear list. It's meant as an example to work from. Look for cheaper subsitutes, especially clothes. Yes, it's expensive, but for 10 days out, it's no more expensive than other vacation alternatives. And the gear can last more than 10 days. All the gear can be bought at REI.