using conglomerate rocks (sedimentary rocks) and dried wood

nope, not safe

No, not safe, if it crumbles, or reacts to muratic acid, you dont' want it in your tank.

I just go pick up rocks I find outside. I boil them twice in saltwater for about 10 minutes.

Smooth rocks are usually safe.

You can usually get rocks cheaper at a landscaping supply store, things like slate and river stone.

I've got a conglomerate in my tank. Did you mean to say carbonate? You don't want any carbonate rocks in your tank because they will leach minerals into the water. Conglomerate rocks are river rocks and should be just fine. If in doubt, do the vinegar test or get some acid solution.

Here are a few things to look for/ look out for in wood:

Never use treated lumber, whether treated for weather resistance or insect/fungal resistance.

New wood can release tanins (mostly tanic acid). This will soften and darken your water and possibly lower the pH (depending on how hard your source water is). Depending on what kind of tank you want to keep, this could actually be desirable.

Old, dried out, sunbleached driftwood is probably safe. Anything problematic has long since been soaked out and UV sterilized

Avoid Oleander and Hemlock (especially if you're a philosopher )

If you have doubts about the wood you want to use, you can boil it in a big pot on the stove, changing the water a few times OR just leach it in a big tub outside, dumping and refilling daily for a while. Boiling is quicker, but leaching has the advantage of requiring no explanations to the missus

cypress not cedar

You can use cypress but not cedar, I think, someone correct this if incorrect. You want wood that has ben submerged or aged enough that all that is left is the ... lignin? the stuff that won't decay easily. Dry wood is not enough I dont' think. Dry wood will float and is likely to decay in the tank, we've seen several account of the inner core of wood rotting, creating toxic materiasl int he tank, including nitrates, and poisoning fish. When removed the wood was stinky.

Rocks, what I recall of the session at Aquatic Gardeners Assn convention in Dallas... nothing that has metalic bits or is shiny, nothing that crumbles when dug at with a knife, nothing that reacts to muratic acid.

Carbonates are OK if you have hardwater cichlids, but not in planted tanks where the pH effect will be a problem. So, holey rock is fine there, the other limestones that you find at local rock yards may be OK, I don't really know.

Slate, pertified wood, granite are safe. Others I can't recall, sorry.