How do bonuses from equipped items, like XP outfits, stack with other sources like Avatar, portable skilling locations, and RAF?

 

At the moment, I'm trying to figure out how much money I can save using Botanists outfit, Avatar, and to determine if RAF is worth 2 bonds (this already seems like a no unless I was doing another skill along with Herblore, but I still want to know how it stacks.)

 

EDIT

I was hoping it would be as easy as, say,

.06+.06+.10 = .22

Multiplying the GP amount RSWiki's calculator gives me by .78...

Yes usually bonuses stack additively. There are a few exceptions, like brawler gloves for example stack multiplicatively, though I don't think it's intended.

In terms of refer a friend, avatar, and skilling outfits,

Since RAF supposedly stacks with skilling outfits I would assume that affect the base experience to 110%. I believe outfits and avatar go off the base experience. I could be wrong though.