I have searched and searched for the empty flask and the last Monkey Idol. I don't think I have ever had the last Monkey Idol, but I did have the flask but I didn't know you had to keep it. I have searched and killed everyone everywhere and have went to the towns and still haven't found them.

There are lots of empty flasks in the serpant temple which is the only place you will need one to collect the spider nectar. All the idols are in there too and again this is the only place you will need them