I'm pretty sure this is Dragonworld (1984). I'll be quoting from this Gamefaqs walkthrough a couple of times during this answer.
I remember it as being an Interactive Fiction kind of setup with typing in commands (GET MAGNIFYING GLASS, GO EAST, etc) with drawings at the top of the screen ... raw in place with lines, I think, largely dark and few colors if not black-and-white
Mobygames has screenshots of the various versions of the game. The PC version did indeed have very few colours, just shades of purple plus black and white. (I understand that this was common among CGA games; something I didn't know until a few days ago):
Whereas the Macintosh version was black-and-white:
There were also Apple II, C64 and MSX versions of the game, all with a lot more colours than the platforms above. The MSX version may only have been in Spanish, going by the Mobygames screenshots.
The opening was an action sequence where you were trying to navigate your raft from the top of the screen to the shore at the bottom using the arrow keys, avoiding hazards on either side of the channel. I don't remember if this was something possible to win or lose.
After the page of text, the game began with you having to step into a boat/raft, raise the sail, and then enter directions. In all the walkthroughs and screenshots I've seen, the player just entered 'E' to go east, and was immediately told that the raft had crashed. It was necessary to crashland on that particular shore to continue the game, so I don't know if there was any way to "win" that part either. But it's still playing like a text adventure here, not the action game you remembered. Perhaps an action subgame might have happened if you'd entered something other than 'E'?
I remember the beginning had a page of text explaining why you were playing. I think that it was your standard fantasy setup with the evil wizard in a tower.
It did have a lot of text at the start, although the plot was more "a dragon has been kidnapped and is being held captive somewhere!" than "There's an evil wizard in a tower!"
One of the items was a magnifying glass, which I think was used to ignite some brush.
As seen in this Youtube video of the Apple II version:
The walkthrough I mentioned uses a different verb ("Take" instead of "Get"), and has the player get the jewels and underbrush in a different order, but it still works in the same way:
You gather some dry underbrush together and leave it in a small pile on the roadside.
You gather a few that have fallen to the roadside.
You take out the magnifying glass that you carry.
The smoke curls up into the sky. The windship spirals down towards you. A rope ladder is lowered.
Cutting to the other scene you remembered:
I mainly remember the magnifying glass because there was a scene where, if you entered a village, you joined in their festival and succumbed to food poisoning after which they carried you to the outskirts and left you there, with someone pilfering the magnifying glass from you. I have a fairly vivid memory of that screen, up at the top of a hill with trees to one side, and the village down at the bottom of the slope.
Let's see how this screenshot matches your memories.
You and Hawkwind are in the bazaar of Kandesh, a huge dirt floored tent filled wth stalls and wagons. North is a physician's wagon; a tailor's booth is to the northeast, east is a moneylender's tent, southeast a makeshift tavern, and directly south a gaming house.
It's not actually a festival - this set of tents appears to be an everday thing in Kandesh. There appears to be a slope which could be a hill, and one of them might be on top of it, but the rest are on the sides of the hill. And there are trees to the side of the hill, like you remembered.
You'll visit this location a couple of times in the game; this is the first one. You do get robbed when you visit the tavern, although they don't take the magnifying glass - just all of your money:
There's no mention of food poisoning, but since this happened immediately after the bartender gave you your drink, you might have misremembered it as being poisoned. Your character is taken straight to the doctor's after this happens, but that's to treat injuries sustained during the fight:
In the text at the bottom, the doctor is telling you that you'll have to leave one of your posessions with him. Perhaps you decided to give him the magnifying glass? In the walkthrough, the player just gave him some leaves.
Now, later on in the game, you return here. On this second visit, the game informs you that "Suddenly you realize how hungry you are."
The player in the video decided to sit down at the restaurant and order some food:
As you can see, no harm came to them from ordering the soup. Perhaps if they'd chosen one of the other items, they might have been poisoned? That "coldrake pate" sounds suspicious!
Let's see how another Let's Play handled this scene:
And indeed, just as you remembered, food poisoning! Passers-by carry you to the physician (not the outskirts), and then you discover... you've been robbed!
Your money was stolen, but not the magnifying glass. The Let's Play-er decided to go back to an earlier game state so they could choose the soup instead, meaning I didn't get to see how this would have played out. That said, they did visit the locations in a different order to the Apple II LP-er, and so they were later robbed again in the tavern brawl. They gave the magnifying glass (now called a "magnifier") to the physician, so it can't have been stolen there:
And with that, we come to the end of this answer!