That sounds like a good idea since the second volcano, next door is expected to blow soon.

This sounds like an interesting event to prepare for. It appears to me to have many things in common with a CBR Warfare contamination problem. Your version of Civil Defense might be the best place to get checklist suggestions for dealing with this Ash Cloud Problem. I would think that a 1-2 month supply would be advisable. I have NO EXPERIENCE on this particular subject:

Let's see:

SUPPLIES:

Shelter: Multiple N95 masks, Multiple bandannas (large), Visqueen to seal off window and door drafts, sufficient duct tape to hold visqueen,

Water: Fresh water stores at home, container to carry water during workday,

Food: 1-2 months of canned food (or food in dustproof packaging?/MINIMUM),

Heat/Cooling: Ability to heat the home in winter or cool it in summer?, Heat to prepare food and purify water,

Miscellaneous: Brooms, ladder (to sweep roofs daily), First Aid Kit, Multiple spare air filters for heating/cooling systems and machinery on hand, Flashlights, battery operated or crank radio receiver, spare batteries in required sizes/voltages, An air pump to supply filtered air into a home and the required piping to remove CO2 from the home,

MAINTENANCE:
Sweep roof daily during periods of ash fall.
Sweep ash from automobiles and other equipment.

QUESTIONS:
Does ash cause problems with power transmission lines?
Will ash cause problems with civic water processing and delivery?

That's my 2 cents worth, off the top of my head.