"I imagine someone in the group will be bringing something.
What I may be interested in is a small canister for myself to keep on me or in the daypack. I can see where they would not have the range of a larger spray bottle but other than that, are the pocket sized ones worth having?"
Okay. I'm not sure you realize the gravity of a situation in which grizzly bears WANT to eat you. A full grown grizzly that is truly charging for blood will travel 30fps. That's right, 30 feet per second! Their head will be bobbing up and down so fast you won't likely have time to even take aim, be it gun, flare, or spray. This is the reality of the situation that KILLS. If you are in this situation, you likely just surprised a bear or got between her and her cubs. Your best defense is avoiding blind corners and staying alert. Since you are in a larger group the chances are even more so in your favor.
Now take all that into consideration, plus the wind, branches, leaves, brush, the bobbing head of a charging bear which makes it impossible to hit them in the face on the first try… etc etc. GET PROPER BEAR SPRAY WITH A PROPER RANGE AND VOLUME. You will not do anything but enrage a grizzly otherwise. It takes more than one good blast to discourage a bear, even if you do manage to stop the first charge with the smaller spray canister they often do and may very well come back with an even more aggressive subsequent charge(s). Hopefully the experienced guys you are going with understand what a feint charge is versus a serious life threatening charge.
Grizzly has up to 6 inch thick bone plates with no weaknesses except for a 4"x4" box centered on the nose and their exposed shoulders as they drop their head during the charge for about 0.5 seconds before they are on top of you. There is no rifle that will absolutely punch through that skull except for the 45 70 with very specific rounds designed to cut into bone, versus glancing off. Many many hunters in alaska have put perfect groupings of up to 7 rounds in bears with 45 cal side arms, to be found half eaten inside a bears corpse miles away from the shooting. Grizzle bears are no joke and will not stop their charge once they are enraged by you. If you don't have proper force you are better off taking the odds that it is a feint charge. Do not assume any gun or anything will stop them.
Not anyone can just pick up a 45-70 high grain round and squeeze off a few shots perfectly, this takes practice. I don't recommend bringing one unless you're proficient with it. Don't bring ANY guns except a 45-70, can't stress this enough. You're better off leaving them at home and going in with just the BEAR spray. Anything smaller will likely cause more problems than solutions in the event of a bear charge. The worst problem being a false sense of security.
These are all facts straight from a guide in Kodiak Alaska (1 grizzly/sq mile). He has had to shoot 3 bears, one of which nearly killed him after he put 3 shots into it with a "high powered" rifle. After this event he never goes back in with less than a 45-70 and never recommends any less to people that ask. He also stated that with one swing of his arm at the bear, it intervened before his fist got even near the nose and had completely ripped all the muscle from his arm. This was in the blink of an eye. The shaking was so violent that he stated it was impossible to even cock the hammer back on a side arm let alone get a shot off. He also mentioned how the bear had cleared all the small trees in about an 8' radius with him, during the violent shaking it was throwing him through trees up to 3" thick. He survived by the grace of God, nothing less. In the other shooting it took 5 shots from a 30-06 and he said even after the third shot took out its shoulder it was still coming at them alarmingly fast on its belly and 3 legs. The final shooting was from the side, while the bear was mauling someone he shot it in the spine.
The exception to the 45 70, if you really must know, would be in the event that you planned only to shoot the bear in the spine. This means it will be on top of someone before you get a chance to take it out. This is often how people are actually saved from grizzlies versus defending during the charge. Many people believe they are better off risking a real charge than turning a feint charge into a real one 100% of the time. This is why you need a gun that can punch holes in 6 inch thick bone, and or blow out a shoulder in one shot. Anything less will just enrage that bear and once that happens there is absolutely no stopping it unless its dead or your friend shoots it in the spine while you're mauled.
I don't mean for any of this to discourage you but I just want you to realize the actual situations we're talking about when we talk Bear spray. Do not attempt to use anything else or you are causing more problems than harm, period. The bigger bears get the more human they become. They are not hunting you, they don't even want to be near you for that matter. If you scare a bear, it will react as described above. If you remain alert, the situations in which people are mauled are nearly 100% avoidable. Not only this but remaining alert will give you the opportunity to observe one of mother nature's most inspiring creations in safety and confidence. Bears truly are amazing creatures and not something to be feared. However, remain prepared.
You're more likely to be attacked by a moose than a grizzly. Moose kill a lot of people and are much much much scarier than grizzly bears in my opinion. A moose charging you is not going to stop until you're dead and they don't bluff charge and they are absolutely NOT afraid of you. Hopefully this won't be an issue during the season you're headed in.