1. Watering can. I have two, one large and one small. This extends your reach on your hose and keeps you from undoing the exquisite hose wrapping job you did the night before. Great for hitting potted plants or refilling birdbaths.
2. Hose nozzle. Get a good one. A good nozzle should not clog, leak, and will reduce hand fatigue for those really long watering sessions. Avoid plastic (dont get me started...).
3. Hori hori knife. I'm on my second one. This great tool works as a weeder, a bulb planter, a trowel, a root cutter, and when necessary, a weapon.
4. Hand pruners. I still have my first pair of Felco F-2s. Keep them sharp and your wrist will thank you.
5. Garden shears. Sure, you could get by with using pruners, but sometimes you need a nimble cut. I use these for cutting twine and for harvesting veggies and herbs.
6. Weeding tool. There are a lot of options for weeding tools. I like this one with a curved, serrated blade. In my larger beds I'll opt for the hori hori knife, but this guy wins for getting between patio stones.
7. Hand saw. Another pruning tool, I use it for keeping trees tame and cutting up debris from storms. Mine is also by Felco.
8. Sunscreen. The next few aren't so much tools, but I don't garden without them. Sunscreen is essential. Time will get away from you, and before you know it the sun has you cooked (=wrinkles).
9. Eye protection. Used when running a trimmer, cutting up wood, pruning trees, and mulching on windy days. Nothing sucks worse than getting shit in your eye.
10. Gloves. Without a doubt my number one tool on this list. I don't want gnarly callouses, don't care for holly needles, and appreciate it when I can still feel my fingers when working out in the cold. I like gloves that "fit like a glove"...I need my dexterity and nimbleness when pulling weeds or training shrubs. These are by Youngstown. I go through about two pairs a year.
11. Hearing protection. I've lost enough hearing from standing beside amplifiers. I don't run any power equipment without these, including my electric grass trimmer. You can modify yours to look badass while wearing them. Just add skull and crossbones.