A Brevet is basically a fast paced, self supported dirt tour, which you happen to be completing along with a few new 'best friends forever'. The emphasis is on self supported aspect... no outside assistance is allowed, no caching of food or water, no staying at a mate's place or enjoying a roast cooked by your Mother-in-law en route! Yet, using commercially available businesses for accommodation or resupply is ok.
As such, gear selection is a topic worth considering. Now the thing is, you want to carry as little as possible yet you need to be able to recover properly at night, and ensure you have enough spares to get yourself out of a sticky situation. Carry enough equipment for your experience level and tolerance for suffering.
Generally the preferred steed for these adventures is a 29er rigid or hardtail but to be honest the bike you ride the most, as long as it’s comfortable for long long hours in the saddle, will be perfect. Wide tyres (but not fat) set up tubeless tend to roll the best.
Carrying your gear is typically via bikepacking bags such as the Ortlieb Seatbag and Handlebar bags. These are the lightest option for attaching everything you need for multiple days in the saddle to your bike. Avoid carrying anything on your back, as the added weight can cause a few issues in the nether regions. I carry my sleep system up front: tent or bivi bag (weather and course length dependant), sleeping bag, sleep clothes (dry socks, merino boxers and merino tee shirt) sleeping mat and total luxury item (but for me now a necessity) an inflatable pillow.
Out back, in the seatbag, I've got some (limited) spare clothes - an insulated jacket, waterproof jacket and trousers, warm hat and gloves, limited toiletries, a first aid kit and some food. On the top of the seatbag (facing towards the sky) is where I carry my SPOT GPS tracker.
My spare parts fit in a small puncture repair kit container. Typically these include a spare cleat and bolts, couple of chain links and quicklinks, brake pads, chainring bolt, tubeless wheel valve, valve core remover, and a couple of spare bolts. I also pack a multi tool, chain breaker, spare cable, several cable ties, a tyre boot and puncture repair patches, some Duct tape and a small bottle of Stans tubeless fluid. I carry 2 spare tubes strapped somewhere on my frame.
Unlike conventional touring I don't cook any hot food and so reduce weight with the associated billy and cooker. Planning around eateries and resupply stops is very much part if a successful Brevet strategy. There may be some long stretches without resupply options, thinking through the options is important. You should only carry enough food to make it to the next resupply point. Being aware of opening times is important, especially in rural New Zealand. Sometimes I’ll make an exception to the 'nothing on my back' rule and break out my Osprey Ultralight Stuff Pack and fill it with pies and bacon sandwiches to get me through. I carry my water in bottles (2 x 1l, 1 x 750ml) although plenty of others use a bladder in a framebag. My food is stashed in various pockets, pouches and crevases on the bike and me.
Other miscellaneous items I carry include a headtorch, wet wipes, sunscreen, lip balm, loo paper, chafe cream, pocket knife with scissors and tweezers. Move fast, but take the time to smell the honeydew and enjoy the flat whites.