I think it depends on the form the LARP is taking. In the system I'm part of, we assume that the spells are mind affecting, therefore you can't dodge them (so no need for the bean bags) - BUT the spells can be resisted due to personal conditioning or personal heritage.
Some examples used in our system:
-> Elves have natural magic, therefore they are used to it and they can "resist" a single spell
-> Some mercenaries have been around magic to "suffer" the effects, so they can resist a spell
-> Mages would recognise the effects, therefore they can resist a number of spells at the cost of their concentration on other spells.
-> Certain races are immune so some spells don't work at all, but they can't resist others
-> Some knightly orders are either trained out it OR are given protection from the gods - so they are immune to things like FEAR.
But since we don't have "magic missle" or "fireball" in game, we don't need projectile magic spells.
Like I said - it depends on the style of LARP the system you're part of would govern whether spell packets are required.
- Elves have natural magic, therefore they are used to it and they can "resist" a single spell.
- Some mercenaries have been around magic to "suffer" the effects, so they can resist a spell
- Mages would recognise the effects, therefore they can resist a number of spells at the cost of their concentration on other spells.
- Certain races are immune so some spells don't work at all, but they can't resist others
- Some knightly orders are either trained about it or are given protection from the gods, so they are immune to things like Fear.
I assume the reason why bean bags are used is to keep track on the spells you have. In our system, mages have to prepare spell cards, which are ripped when a spell is cast and you. You learn to keep a tally in your head of what power you have left. But, since we don't have "magic missle" or "fireball" in game, we don't need projectile magic spells.
The style of LARP system you're part of would govern whether spell packets are required.