Paper - virtually anything goes but if you use a lighter weight paper it is important to flatten it under a book after a layer is dry. I like to save cardboard and gesso over it and if I'm in the mood to splurge I buy handmade paper from Etsy.
Adhesive - For 99% of anything I need to glue I use glue sticks. They are inexpensive and are very durable once the glue dries. If I am adding a 3D embellishment I use a glue gun. For larger areas I recommend YES! Paste. Its very sticky but does a good job without buckling the paper too much.
Paint - Acrylics in tubes are my go to in most cases. You can get a fairly inexpensive set at any local craft store or online. Craft paints work well too, especially for covering large areas of a page. Watercolors are not necessary but if you do want to use them I highly recommend spending the money on a decent set such as Paul Rubens or Winsor Newton as they are highly pigmented. Cheaper sets will not give you rich colors.
Brushes - I like inexpensive synthetic brushes with nylon bristles. You can usually find a set with different sizes that are inexpensive at your local art supply store or online.
Ephemera/Stuff - In creating backgrounds for my work I like to use a random assortment of papers. Old newspapers are fantastic as are vintage magazines. I save envelopes, and other junk mail as well. Sometimes I use stickers so if you have some go for it but it's not necessary. If you want a cheater's way to make something look vintage you can paint it with a light brown watercolor wash or run a brown stamp on it. I sometimes use more three dimensional objects like buttons, pieces of old jewelry, feathers, scrapbook materials, anything you find in your junk drawer (!), etc.
Markers - Any set of gel and/or paint markers are a good place to start. That being said in order to get some of the specific techniques to work that are two must have markers in my toolbox. The first is a Tombow watercolor marker. It has two ends to draw with and when you add water it's almost magical! In order to get a white outline on a darker paper the only marked I have found that works is the Uni Ball Signo Um-153 in white.....trust me I've tried many!!!
Other - Rubber stamps, washi tape, decent pair of scissors, white gesso, any my personal all time favorite random tool.....a brayer. Brayers are traditionally used for printmaking but I adore using them to spread paint on a page.
When it comes to mixed media art pretty much anything goes so if you have something that I have not mentioned please go ahead and use it. If you have any questions please feel free to message me on Facebook!