(Small Gods by Sir Terry Pratchett, right?)

I, a simple tortoise, learn to fly.

You drank a little too much of [insert favored alcoholic beverage here], and you're head's feeling a little too heavy with liquor. For some reason you find yourself on a ladder a few minutes after finishing a drink, and you fall from the ladder and burst your skull open. No one with medical proficiency or even the slightest bit of common sense is around you, so you're sure to die from blood loss and blunt force trauma soon. (EXTRA bonus points if you know what book this is from. If you do you're a madman.)

I confidently think it’s from cloudy with a chance of meatballs.

as I am falling, I quickly text my doctor the Address of where I am about to crack my head open, and then I do a quick backflip to make my fall look cooler.

minutes later an ambulance arrives and they find everyone cheering my backflip (no common sense)

You were walking your black cat, and after walking under a few ladders, you realize your mistake too slow,  and your bad luck culminates into summoning an air strike against you.

(Small Gods is right)

It's an air strike. Air isn't too hard. So after standing through a slightly rough breeze I comb my hair back in order and break a couple mirrors. 

You are in a mirror dimension when someone just broke the mirror your mirror dimension was in. 

I cast mending on the mirror. 

You are a human commoner and you just got decapitated. 

Actually, I'm not a human at all. My head is just a ridiculously well-disguised tiny Beholder, and my body is that of one of its smaller captives. My eye-tentacle-things were tucked under a hat, the non-existent 'neck' was obscured by the standing collar of a trench coat, and my mouth was covered with a fake mustache. As the executioner brought the axe down it sliced the space between the two of us.

You, an executioner (equivalent of a level 1 fighter), just decapitated a human. Said human was really just a beholder (+ captive) in disguise, and now seeks to take over the town.

I summon the TERRASQUE to come eat it.

a massive terrasque just walked up to your town, and you see it just ate something. After it finishes, it walks through the town, wreaking havoc, frozen in fear, you get stepped on.

The tarrasque was a fool! I am a gelatinous cube on by stepping on me it has fallen into my trap! Now I am slowly digesting the tarrasque. It'll take time, but my victory is inevitable. 

You are a door-to-door mirror salesman and your most recent attempt to sell just took a bad turn: your desired customer is a banshee.

Oh no. I close the door and begin running, then I think, do they pay me enough for this? Doesn’t matter because I’ll be dead soon enough, but then, to my surprise, the banshee actually buys the vacuum.

you just got hit in the head with a brick

It was a lego brick. Very small compared to my head. 

You are a simple pine tree, being chopped down. 

I have two ways of preserving my life. One through mushrooms and another through a cutting. I've lived a good, long life as a full-grown pine tree, but it's high time I got a newer body. As the people that are chopping me down are doing that, I send my life essence and wisdom to the mushrooms in the ground to be given to the trees in the area. Then, assuming a branch or two of mine falls off during the chopping process, I clone myself and root as a brand new pine sapling via the fallen branches. The mushrooms give me back my nutrients and life essence and I go back to living life anew.

You, a woman on a pirate ship, have just been tied up and are to be sent to the fathoms below for bringing bad luck to the ship (even though that's not true).

The first mate reveals that they are a woman too and leads a mutiny against the captain! She wins and makes me her first mate, and together we become the scourge of the seas!

 You are trapped by a falling tree in a forest fire.

I wildshape into a beaver and devour the tree with my teeth

You're minding your own business being a beautiful pine tree, when you are set alight by a forest fire and are now being devoured by a beaver.    

Oh no! I quickly fall over into a lake (unintentionally) and, after the beaver lets go because it needs to run away from the fire, I stay in the lake for a few days, until a wizard with true Polymorph, decides to turn me into a human, years later, I am now Derek, the tree Druid.

you just took the medicine the Druid prepared for your broken arm, when you realize that that wasn’t the medicine, that was the rest of your sovereign glue. now you are suffocating and most of your internal organs are not functioning, from the indestructible glue coating them.

I have a vial of universal solvent, which I drink. It quickly dissolves the glue. Then I ask the Druid to cast Lesser restoration to take care of any residual effects of either.

You are a cat familiar, being sent to scout ahead, when you stumble into a pit trap lined with spikes. Kobolds begin to snipe at you with arrows.

The person that I am a familiar for is pretty reckless, so I die a lot. I'm used to it; they'll just re-summon me again in a little while.

You constructed wings of wax, and decided to fly over the ocean with them. You fly a little too close to the sun, and your wings start melting. There is no land for many, many days' worth of travel.

I am in a myth, and I survive through the countless retellings of my story.

You are a book someone is reading in a rainstorm and you are dropped in a puddle.

I'm one of those toddler bath books. Being in the water is me being in the zone. 

You arrive home to find your pet tiger has escaped its cage. 

I whistle, and it comes to me in a flash, entering its cage when I direct it to like the well trained pet tiger that he is. 

You are crammed in a 10'x10'x10' elevator with 30 other people, and it has been going up for a day now, seeming to be cursed to never stop or let anyone out. 

I pull out my portable hole, quickly blow my nose with it, and throw it in my bag of holding, sucking me and everyone else into the astral plane. With my incredible luck, we appear right next to a spelljammer ship, and after a long voyage, we finally get back home.

you are a werewolf, and you just smashed into a silver mirror, dealing you fatal wounds.

I cast remove curse on myself, and if that doesn't work I cast wish. Then I rest. 

You are stranded on a deserted island and you are a wizard without wish or any teleportation spells