What features do you look for in a MTB hip pack

I have never considered a hip pack, so I'm not really your customer. However, if I was looking at one, I'd be greatly swayed by innovative features that competitors may not offer. A quick-access phone sleeve would be cool. If you could make the tool pouch side divisible with partitions, that's interesting too: I don't know if I'd need a whole pouch just for tools, but a multitool and a GoPro would probably go in it. It would be nice to protect the camera in a different compartment. 
I would probably prefer a water bladder over none. 

Features Needed: 

(I may re-sort into order of importance. These are listed as they occur to me, which is relevant in and of itself,  but often not the same)

pockets on the sides, for easy quick access. (very small)

buckle / belt fastening off set to one side.

internal hook for car keys

Decent place for phone (harder than it looks)

external straps or loops or both

easy to pull zippers

naturally curved shape

some kind of internal sorting / storage / mini pockets (very flat if not used, nothing "heavy duty)

some place to put your name across the back, like cowboy rodeo belt.

I like the EVOC hip pack I use. The wide belt across the front makes it more comfortable than other hip packs. I find it is more comfortable without the water bladder installed even though I carry 2 large (24oz IIRC) water bottles in the bottle pouches. The bladder pushes the pack away from my back and it loses stability. 

I like hip packs since I find it easier to keep my shoulders relaxed without pack straps over them. 

I went through several hip packs before I found the Osprey Savu 2.  It holds just enough tools and spares that I'm comfortable and a water bottle.  I like that the water bottle is on a slant in the center.  It makes the pack balanced and I can easily grab the bottle while riding.  

I won a Dakine hip pack at a race once.  It was a bladder style.  I wore it on one ride and it was terrible.  It felt like having a 2x4 strapped to by back.  When you filled the hydration pack it didn't leave enough room in the pack either.  One thing it had that I really wished the Osprey had was a small loop to hang the bag from near the latch on the strap so it could hang vertical.  The Osprey has on in the center and it takes up so much more room to hang in the garage.

#1 feature is not being a hip pack.  I've tried several and they tend to move around a lot (especially loaded) and pressure the lower stomach uncomfortably on long pedals.  Vests are far superior.

Carry extra water bottles.  That’s biggest thing.  I pretty much much only use one if I need more water than I can carry in my bike.  

Before I started wearing a half bib on bigger days instead I was planning on making my own fanny pack.

2 zipper pockets.  One lg main and one padded waterproof for phone and keys.

Was planning a simple loop system for attachment to either a belt or to the frame on top tube with a loop on one end to secure to head tube.

Either use the main pocket for a bladder or a tool bag.

Wide belt not a skinny one.
Pockets big enough for a snak bar or gel's on both sides of the waist where the bel comes around.
wide opening for the bladder pocket to assist getting a full bladder in.
fidlock type connector to hold the hose/nipple in place. 

Completely agree. I hate wearing those things. They don't carry enough and they're incredibly uncomfortable on long climbs and rough downhills. I prefer Osprey backpacks that sit away from your back and allow good airflow. 

Not even! If your shirt can’t flap in the breeze it’s not worth leaving the couch. Backpacks are beat. 

 

I’ve tried many hip sacks over the years and with every new purchase have trended more minimalist. My current go to is the Evoc trail belt. This belt has all of the features I want and holds everything I need for rides up to 15-20 miles. I just would like to see some of the features more well executed. 

Feature improvements and general needs
The phone pocket needs to be a 1/4 larger to easily fit a standard size iPhone with a case

The belt should be a 1/2 - 1 inch wider

The pockets should reflect real world use and be tall enough for a 16gram co2 with the head on it. One of the 2 tool pockets should have a more secure closure than the current Velcro                

The food storage could increase in size slightly The key/wallet pocket is good but could maybe be smaller.

A place for everything and everything in its place. Nothing clanging around. Just enough space for the essentials while keeping it light and tight to the body and under the jersey. 

The securing mechanism needs to fit tight and stay tight. I hate it when a hip sack sags down through the ride. The Evoc pack has Velcro and a buckle which seems to outperform all other options from my experience. 

Everything, especially food, needs to be easily accessible from the bike. I like to move quickly through the mountains and often prefer to not stop to smell the flowers.

Things it does not need (for me)
A hydration bladder. 
Large open space 
Traditional water bottle carriers.                 Capacity to carry MORE
To be seen

On the spectrum of mountain travel I lean towards the light and fast side vs. the kitchen sink crowd. For context I use a hipsack for rides under 2.5 hours. On longer rides I will use a vest style pack sometimes in conjunction with XC kit with the additional storage of jersey pockets. I also always have a tube and often pump/co2 on the bike. Additionally if I need it I can easily fit a large 1000ml bottle on all of my muscle powered bikes.

I can carry a 6 pack in my backpack and share with friends at the top. I've never seen anyone with a hip pack sharing beers at the top.

Definitely not interested in this behavior.

Rmu 1L is a good example of a featur rich small pack

I’m skinny, hip bags don’t work. Always move around, don’t fit and are annoying. 

I like my USWE pack, but the hydration tube could be 4-6" longer. Also no room for a pruning saw or anchor spot to strap one one.

Last week I dug out a 25yr old Mountain Smith Tour pack for a trail work day. It worked surprisingly well and held 2 water bottles, with a loose 6-pack and pruning saw inside.