Rick, sounds like you've got your gear pretty well covered. But I agree with Max. Since you've got a tripod for your 600, I really don't see the need to bring a monopod. Unless of course, you enjoy being a beast of burden when you're on vacation (hee hee). The 100-400 is usually my go-to lens when I'm in the Park because of its versatility, outstanding image quality and it can also be hand held which will give you the freedom to move around at will and shoot spontaneously, without having to carry or waste time setting up your tripod. And if a support is needed, you can always look around for a natural support to use (ie: a boulder, fence, rock, a tree stump or even a big tree limb. That's what I do. IMO, a natural support tends to work better to stabilize a camera setup because the support is grounded, eliminating vibration. I use the 100-400 for taking pix of all sorts of Yellowstone subjects: animals, birds, mountain and thermal landscapes, wildflower close-ups, butterflies, tree bark and fungus, ferns, bushes, water lilies, rock formations, water (pools and riffles), high-flying rainbow trout, terrestrial insects, bugs and, even, creepy crawlies. Because the lens has such a wide range of focal lengths, that will give you an opportunity to use your creativity and imagination when composing pix. In other words, you'll be able to "look beyond the lens" and think out of the box. That's why I love that lens. With the 100-400 IS II matched to your 7D 2, you're going to have the perfect Yellowstone setup. And if you're concerned that your tripod won't be able to handle the weight of the 600, put some rocks in a plastic grocery bag and tie the ends of the bag to the tripod. If your tripod has a hook under the plate, you can tie the bag of rocks to that. Works well when it's windy....and we've had plenty of wind in the GYE lately. In fact, we've got a flood warning that begins Sunday for all the towns along the northern slope of the Beartooth's. Rivers are really raging right now.
If you want to simplify the gear for your trip, Rick, and want to lose some of the carry weight, and have fun being creative at the same time, here's my suggestion....(just some food for thought). Bring your tripod and gimbal head to support your 600 for photographing distant wildlife and birds and then use your 100-400 with or without a TC and a natural support (if needed) to photograph everything else. For me, photography is just like fly fishing. You can spend thousands of dollars buying the best equipment and fancy duds but if you don't have good technique and can't make a decent presentation of your fly to a fish, then you aren't going to catch a fat and feisty cutthroat.
The same holds true for wildlife photographers. If you don't approach an animal correctly and gain their trust, then you may as well stay home and watch the Stanley Cup playoffs.
We won't be going to the Park until mid June, Rick, so it looks like we're going to miss you again. Hope you have a fantastic trip! And check your PM's when you get home. I've got something for your gear repertoire that you might be interested in.