Substitutions for ritual ingredients

[mikastophiel]

Hello all, I was recently a bit annoyed as a spell called for agarwood and mastic, which my financial situation has rendered a tall task, which got me wondering how y'all get around some of the more tricky-to-source or expensive ritual ingredients that old spells or grimoires can call for. I know some people use substitutions based on celestial correspondences or make spiritual proxies, but I'm sure there's some methods that have slipped my mind.