Potential sources —

Sulfur/brimstone: is found in near volcanic vents or as underground deposits. in game this might translate to on the walls ceiliongs near lava (but the sulfur blocks should be flamable, not clear on how to handle this — possible impose a distance requirement so that sulfur doesn't 'deposit' within the fire spread distance.)
Whether this should be a wordgen only material or something farmable (possible via a reversal of teh dripstone model with some form of sulfur collecting block a distance above lava slowly collecting teh materaial.)
Historically, sulfur has been associated with the judeo-christian Hell (hot version/areas), but adding it to MC's nether could be problematic due to the potential for fire.

Rose: Already in game

Glass shard: dropped when glass blocks/panes are broken without silk touch would make sense; somethng similar to the sea lantern / crystal set-up could be used.

Pebble: potential drop from mining gravel without silk touch (à la flint) How ubiquitous this should be ought be in [​rough] inverse proportion to the utility of the item.

Basilisk Scale: Presumably harvested as a drop from a basilisk kill, bot possibly via some other mechanism (e.g. turtle or armidillo scutes)

Hairbrush: crafted: wood plus hog bristles (new pig drop)

Leaf: processed from leaf blocks [?] by shearing [?] A single kind?, or one kind per leaf block type? differnt uses/properties?

Bat Guano: found in caves, could be made farmable if it accumulates in areas with bats [​Note that bats are already farmable, just very few people bother.]

Bee's Wax: Already in game

Ghoul Hair: presumably a mob drop, but might also be acquired by a process akin to 'wool gathering' in the appropriate environment

Banana: new crop, harvesting would likely be better following the pumkin/melon model than cocoa or apples

Pebble: similar to snowball but it attracts mobs to the block you threw it at, unless if they are aggro'd to something or can't reach it. It can be harvested by right clicking stone with a shovel, if its normal stone then it turns into cobblestone. While there is no limit to how many pebbles you can get from a block there is a stacking durability drain on the shovel for that block, this is to prevent farming pebbles from a single location.
Glass shard: break glass, lawl. it can be used to craft shattered glass which is just a cosmetic that can be used for like run down builds or something. you can also throw it like a snowball/pebble and its like a early game bow and arrow where its ranged damage with ammunition but it sucks hard, like a long range punch.you can also use them to make glass panes (panes are just flat glass, why does it need 6 full glass blocks anyway?) however it doesn't make as many at one time like normal glass does. You could do this for any glass recipe that gives more than one block back actually.
Bat guano: Like bonemeal but an aoe, sort of like using bonemeal on a grass block. it can also be used as fuel, more than wood but less than coal. no reason why I can't be thrown like the others, make it do no damage but give poison for 2 or 3 seconds lawl.
leaf: glass shard but for plants. maybe you can craft a new item called a replica sapling that looks just like a sapling but never grows, for decoration ya knows? you can also feed them to sheep to grow their wool back but they need a handful of the stuff for a single wool regrow.
hairbrush: craft it with ghoul's hair and concrete. its like shears but just for wool, it collects it more efficiently by allowing two clicks on a sheep. you can also use it on cobwebs to get more string and wool blocks to get string instead of the block back. use it on a horse for a chance to apply regen.
banana: new crop but it requires a sapling instead of a seed, the sapling must be planted on tilled farmland still. bananas come in bunches so its like a food that ether be eaten multiple times or when initially picked up it stores like 6 of them at once and breaks apart permanently when right clicked...... you can also throw them and they come back like a boomerang but they have a short range and have a chance of being destroyed on hit. if the throwing idea is actually used then maybe don't make them come in bunches. instead of healing a ton of hunger they just heal half a meat stick but directly heal a heart. they can also be used to make yellow dye.

Feel free to give ideas on sources of these items as well.

Working om the idea this is a new mod (i.e. no constraints due to prior art)

Sulfur: [​aka brimstone]
most obviously, a component of blackpowder (gunpowder)
a fumigant
a bleach (as the [​poisonous] gas sulfur dioxide)
a food preservative
converted into acids (sulfuric H2SO4 and sulfurous H2SO3) it supports a wide range of industrial applications (some of which would be appropriate to your period)
for patinating metal (often as liver of sulfur: a period name for a mix of potassium / sulfur compounds)
pure sulfur can also be used for casting [particularly for biological specimens] as the melting point is ~112C (233F).

Rose:
food additive (mostly decorative)
feedstock for rose oil (one of the major exports of the Levant in period)
beads (rosary beads were/are traditionally made of rose petal pulp)


Glass shard:
improvised knife
scrap glass was quite valuble and so heavily recycled
clear (colorless or otherwise with no/few bubbles or cloudiness) was treated as a semi-precious stone

Pebble:
Shot (cannon or bird hunting crossbows or slings)
used as part of some processes for fulling cloth

basilisk scale:
as a fantasy item this was reputed to be highly useful for armor /shields and brewing poisons and/or antidotes

bat guano:
fertilizer (rare as was generally too valuable)
early balckpowder recipes often used raw bat guano
later recipes refined that material to extract the potassiun nitrate
skin bleach (although crcocadile dung seems to have been more common)

Bee's wax
Candles
waterproofing
sealing stored food
waxing bowstrings and similar
lubricant (rare as too otherwise valuable)
a component of many food, incense, and other recipes

Banana
other than food, these can be used for oil or fiber (including a form of paper), but I don't know enough about arab tech at the time to know if either was being done

My ultimate goal is to have at least five uses for these items.