I really like using large board then making the stencils at home and wheatpasting 'em up. I tend to get pissed off at seams in cardboard so the best paper I've found is the thicker movie posters which are always in blockbuster dumpsters - they're large but good to cut up too. tar paper can be found in gigantic rolls in dumpsters all over the place in the summer after buildings redo their rooftops, that stuffs amazing because it can roll up easily but is still thick (kinda sucks if you leave it rolled up and paint dries tho). use a fireworks (or any) tube to roll up finished stencils to carry around. for wheatpaste I like using gatorade bottles (the kind with the weird top that feels like a baby bottle - good for squeezing it out) and a medium sized brush.
michaels (box store craft shithole) is pretty much a free store and also has the x-acto box sets and other great things, like packs of micron pens and sharpie paint pens, right now im really into their powder paint -throwing it on walls, squirting water to make it drippy and im really into splatter art right now! plus they have elmers aerosol glue which is super useful for intricate stencils because you can have a tight fit to the wall (or wherever) but still peel it off after while having both hands available for other stuff and not having the hassle of tape! oh, and i just saw some "eco" paint/brushes there, whatever that means.
oh! plus they have projectors that are crappy but at least can be free (if you have five fingers - i just put the box in a big cloth bag with a bandana on top and walked out). they're great for needing to trace an image (yer own, letters, something from a mag or whatever) on a larger scale and being able to add larger bridges. the first projector i had i just got from my old school (the big ol' diarrhea yellow boxy kind) as they're all going to digital projectors now. the second one i got was the same type taken from an electronic recycling place (those places are great for other stuff - old photocopiers full of toner which is carcinogenic shit but can make some great dye for art, circuit board to make into whatever (i got a bunch once and made earrings n crap and sold them at a folk fest and made a killing), typewriters, tvs for destroying, parts...)
oh yeah, and check city websites for dates and places for household chemical drop-offs. they gets TONS of paint cans and i've found they'll give em to you if you just say your an artist (ie canvas, not graffiti), poor, and mention it'll cost them less to not dispose of it....