Despite the scary amount of products I own, I use a lot of the same ones on most days. And I've been building my collection for 5 years now, so take a normal amount of lunch items and times it by that many years.
So, if you are getting started, a few recommendations to help you out!
1a. EasyLunchboxes & Insulated Cooler Bag - This is probably one of the best deals you'll find on lunch boxes. You get four boxes, they are dishwasher safe and they have a bag that fits them perfectly, along with a drink, napkin, yogurt, etc. I use them a lot, because of the space layout (try this tag "easylunchboxes" to see some of what I've made).
1b. Lunchbots - Prefer stainless steel to plastic? We have one of these too. I have a Duo which works well for my kids and I've been leaning towards getting the Trio or Quad, just because I like the built in sections. These also fit well into most standard lunch bags, Faith had a Vera Bradley one last year and it worked.
Now that you've got the basics (containers, bag and water bottles), you can always add the cute stuff!
3. Wilton Fondant Cutters - I actually have tons of cookie cutters, including my favorite sets from Williams Sonoma, but for a quick, easy, inexpensive option, check out the cute stuff Wilton has. Most local craft stores carry it too. Their fondant cutters are metal, so they work well on veggies and fruit, along with meats and cheeses. Sets usually have a tiny version, a small version and a medium version. The tiny one is perfect for decoration (it's about the diameter of a baby carrot), the small is ideal for cucumber slicing, the medium can be anything from cookies to sandwiches!
4. Silicone Muffin Cups - I use the Wilton ones because they were the easiest to find. There are tons of cute options--hearts, stars, flowers, but my favorites are still the solid color squares to tuck into the corner of a box. They are ideal to separate food, although they won't contain anything too messy.
Food Picks & Kebab Sticks - These are just cute, perfect for skewering food or holding things together or just making a plain lunch look pretty. Besides all the varieties on Amazon, don't forget to check out places like the Dollar Tree. I have a package of primary colored hearts, 100 for $1. During the various holidays, they sell themed muffin wrappers with pick too. These are paper, but at 25 or so for $1, I'm OK with losing a few along the way.
Now of course, once you start with a few basic items, you'll probably end up wanting (I call it "needing") a whole lot more! But for now, at least you have the supplies to start.