1) A nice solid foam roller. I got a high density 12" roller from Perform Better 3 years ago and it still works perfectly. It hasn't gotten squishy despite heavy usage, and it still makes my IT Band scream. This tool can go with you anywhere and is always useful. Ideally used pre-workout, it's also useful on a day off from the gym when you are at home. You can't underestimate the importance of soft tissue quality!
2) Metabolic Drive Low-Carb from Biotest. This is a great protein supplement that is trusted by many industry professionals. Biotest did a fantastic job making a protein supplement that tastes great and isn't filled with sugars and crap that just add empty calories in the guise of "weight gain". Trainees need to understand that protein supplementation is not just for guys trying to get hyooge. Proper amounts of protein (and carbs and fat, for that matter) play a big role in being able to achieve your body composition goals (more muscle, less fat).
3) Resistance Bands from Elite FTS. These can come in handy for a thousand different reasons! The original use for superbands was for stretching; there are a ton of mobility and flexibility drills to do with them that can really help you unlock your potential. They are also great for rehab/prehab exercises for your hips, shoulders, thoracic spine and ankles. The most badass way to use them, though, is for accommodating resistance: attaching them to a barbell to change the strength curve. There are two ways to use them (band resisted or band assisted) but the idea stays the same. You change the way a weight feels during one portion of the lift. Example: a band resisted squat. In the hole, the weight will feel like whatever is on the bar (lets' say 225). At the top of the lift, when the bands are stretched, you'll feel the weight of the bar plus the pull of the bands. As the band stretches more, the weight feels heavier. What feels like 225 in the hole could feel like 325 at the top. It's a great way to learn how to accelerate a bar through a lift. It's a fairly advanced technique, but can be useful for many people.
4) The Show and Go Training program by Eric Cressey. I was fortunate enough to be a guinea pig for this program when EC was still fine tuning it. I experienced some pretty good results with it, and I'm confident that just about anybody could see results from it. I added 10 lbs to my body and was able to see my abs. I also added 50 lbs to my deadlift in 4 months. The big benefit to this program is the balance, Eric is a master at creating balance out of imbalance and this program showcases that ability. Having someone else write a program for you means that you can't skip doing the shit that you hate. Eric works in variations of lifts that you may be awful at. He programs in plenty of mobility filler exercises, so you can make good use of your rest periods. Speed work. A high pull:push ratio. Everything you can think of, this program attacks. If you're a beginner wanting to get into great shape, Show and Go will help. If you've been in the gym for a while and hit some plateaus, Show and Go will help you break them. If you're an athlete getting ready for a season, Show and Go will help bulletproof your body. I highly recommend it!
5) The website liftbigeatbig.com! Gasp! It's a CrossFit blog! Now ask me if I give a damn? The guy who writes it provides some fantastic knowledge about weight training, and is a big supporter of women training properly. He is also a big fan of eating large quantities of real foods like beef, milk and cheese. My kind of guy. It's a great place to go and learn some things about aspects of training you might not be familiar with. LBEB also has an awesome store where they sell some really quality t-shirts and hoodies. I've already bought one for myself and for a friend!
That's a decent little list to get you going. Check some of them out, and see if you can add any of them into your own training. In the meantime, go lift some heavy shit!