Here are a few other items you might want to consider picking up......

Waterproof Pack Cover
"So my pack has a waterproof coating. That means my gear won't get wet inside, right?" Actually, no. Coatings help, but don't prevent water from getting into the pack. For one, water can leak through the seams. Even if you coated all the seams, water can leak through the zippers, some of which are positioned vertically from the top of the pack to the bottom. And the waterproof coatings sprayed on the inside of the pack material can eventually wear off. Raincovers eliminate this problem.

Many pack manufacturers sell covers made specifically for their pack models. However care must be made in selection, since if you strap gear on the outside of your pack (and who doesn't), you'll want to make sure that the pack cover will fit overall of it. A generic XL pack cover should be large enough to cover all the gear

Most backpackers in the U.K. avoid external rain covers completely and use internal liners instead. The less expensive variations on this theme use heavy gauge plastic bags similar to what you'd see as a container for fertilizer, or as a survival sack. Others have opted for "dry bags", which are actually designed for canoe/kayaking trips. The dry bags are much more durable than plastic, but also weigh more. The advantage of using an internal liner is that you still have ready access to the pack. The disadvantage is that your pack might get quite muddy on the outside.

Carabineer
In the early days of pack design, it seemed that manufacturers were happy to slap a few pockets on the outside and call it day. Is there a way to readily access your water bottle? Yes - if you have a carabineer. You can use a simple climbing carabineer (some folks in the military call them "snap-links", and in Europe, they're called "Karabiners" or "krabs" for short) clipped onto to one of your pack compression straps to carry your water. All you need to make the system work is a water bottle with a screw-on lid with an attached loop. Fortunately, many manufacturers are starting to incorporate special "open air" pockets or water bladders into their designs, so this may not be a consideration.

Travel Sack
Do you fly to exotic and distant backpacking locations? You may be surprised to discover that your favorite airline may not accept your pack as baggage unless it's contained in a parcel that will secure the pack straps. Airlines know their baggage handling equipment (which in some cases, may be people) are not kind to loose straps hanging off a pack. I've heard many war stories about packs that had shoulder straps ripped off, or large spots of grease smeared on the outside. Do yourself a favor. Buy the sack now so you're ready when it's time to travel. Some pack manufacturers make travel sacks for their packs. In other cases, some folks simply slide their packs into a large rucksack.