Depending on the length of your division, I think it’s probably reasonable to carry a bottle of water in the summer. Is it a formal hunter pace or more casual? If casual, I’d get a saddle pad with a pocket and toss in a bottle of water. If formal, then I’d just hydrate well the day before and morning of and have a cooler for once you’re back at the trailer.
I’ve hunter paced with 2 different hunts. One expected cubbing attire, even from non members. The other is about as casual as it gets. For the casual hunt, I’d wear a technical shirt and maybe a cooling bandana. For the more formal one, well, they don’t hold a spring/summer hunter pace, so that’s not a big deal. But basically whatever you would wear to show in, sans hunt coat.
This depends on if it’s formal or not. If formal, then a fleece, fitted saddle pad and conservative tack. If more casual, then I’d use a square pad and my normal tack. I like to add brushing boots on all fours and bell boots at least in front. I do wear spurs and carry either a crop or a fly whisk. Fly veil/bonnet too for that matter. What’s most important is that your horse and you are turned out well, tack is clean, and you are ready to have fun! 