I agree with the general consensus but, like the boy scout motto...."Be Prepared."
I would stock up on masks...the best is model Besten N95...you can still get in Bali but they're jacking the price. I just ordered a packet of 20 from Tokopedia for Rp100,500.
The general wind at this time of year is from the south and east which should blow any ash NW but the wind could change and ash, being very light, can become a problem over any parts of Bali.
It's unlikely that any actual rocks etc would reach outside the 12 km danger area but Mt St Helens, near Seattle, blew out sideways and killed people over 35 kms away.
Here's a check list for American ash fall-out which may help....
http://americanpreppersnetwork.com/wp-content/uploads/2014/04/Volcanic-Ash-Fall-Preparedness-Checklist.pdf