There are a couple of ways to choose thread to use when sewing.
Purchase quality thread. Cheap thread is cheap thread and will not last. Quality thread costs more but is definitely worth it to ensure the quality and durability of your project in the long-run, as well as making the stitching process easier and more enjoyable, especially in the case of embroidering.
Select sewing thread according to the right colour. Once you have decided which type and strength of thread is suitable for your project, you will need to match its colour. This is where it is a really good idea to purchase the entire quantity of thread in the colour you are using to ensure that you keep the same batch colour quality throughout the sewing project. If you cannot find an exact colour match, select a colour of thread one to two shades darker than the fabric colour to blend in. Light thread will stand out more.
Another option is using a grey thread, as it works for all sorts of lighter-coloured fabrics.
Unroll your thread and let it lay over the fabric. And/or look at the selvages of the fabric it always gives you what colours you should choose.
Buttons and Zippers
This is what I scrimp and save on. There is a gold mine of zips and buttons to be found secondhand; whether online or in your local Op Shop. I have a stash of these on hand to match any project I am doing. The only time I use new zips is for paying customers.