1) I iron plastic bottles and then put them to use. Cool way to turn them into useful things.
Plastic bottles cost nothing after use and are an inexhaustible material for different ideas. So, you can use them to make a bag with which you can go to the store or to the beach.
But, before work, you need to change the material, that is, make flat pieces from round bottles, and then cut out squares or other shapes from them.
Progress:
I straighten the plastic with an iron.
It is better to take bottles with a straight cylindrical shape, without embossing or bulges; I took kvass bottles for bottling, they have smooth and thin walls.
I cut it into small rectangles.
Then I ironed these pieces through paper in 23 layers at the lowest temperature. As a result, the plastic decreases in size and becomes straight; you just need to adapt how long you hold the iron.
From these blanks I cut out squares measuring 8x8 cm.
Use a soldering iron to make holes every 1 cm. I tied each square with single crochets.
Instead of yarn, I took polypropylene twine for garter in the garden.
I arranged the squares into diamond shapes and sewed them together.
I tied a mug between them according to this pattern and also attached them between the plastic, and tied the halves and quarters of these circles along the edges.
I tied the resulting square on all sides with single crochets.
I knitted the back and side parts of the bag with double crochets.
I connected the openwork part of the bag with the side and fastened them with clothespins, then tied them together.
I did the same with the back.
I knitted the top of the bag in single crochet stitches.
Pens:
Any method of making them is suitable, this is a separate topic. Sometimes handles can be the main decoration of a bag.
I sewed readymade bamboo handles.
Take a look at the result, maybe it will be an impetus for creativity.

2) I bought twine at Fix Price and took plastic bottles. I'll show you what stylish thing I made for going to the store.
Handmade bags, wicker, knitted, have long entered into women's everyday life and are at the peak of popularity.
Using a hook, you can not only use ordinary yarn, but also take material that is sold in hardware stores, such as twine and various ropes. They are great for making bags.
And in the garden departments, polypropylene twine of all colors of the rainbow is on sale. In the fall I bought skeins of red color at Fix Price for 55 rubles. Their strength allows the products to serve for a long time without losing their appearance. You need to pay attention to the thickness of the thread (I used three threads).
I will knit a string bag of an improved style from them. I used plastic bottles as additional material.
Here's how it's done:
I cut the bottle and took the middle part for work. I divided it into three pieces.
Next, I ironed these pieces with an iron at low temperature through a sheet of paper. First you need to try and choose the appropriate temperature regime. The plastic straightens out.
I cut out squares from these blanks, measuring 8x8 cm. Using a soldering iron, I made holes on four sides every 1 cm.
I tied the squares with single crochets in two rows. At the corners I knitted three loops in one hole.
I got 9 blanks, sewed them together and tied them around the edge.
I knitted the other part of the bag with single crochets.
I also knitted a strip 10 cm wide, equal to the length of three sides of the bag. I tied it between two parts of the bag.
I knitted the arms, 47 cm long, separately and then sewed them on by hand. They can be made in any way; readymade ones, which are sold in handicraft stores, or red laces are perfect.
This string bag is suitable for shopping or just as a stylish accessory.
The finished size is 32x32 cm.