The sizes that I buy in are: Pils, pale 2 row (both German typically), and MO in 50/55 pound sacks; Sauermalz, Vienna, and Munich in 10 pound sacks (2 or more if I am brewing a Vienna or Dunkel); carafoam, Carahell, and the like in either 5 or 1 pound bags, depending on what I have in the works for planned brews. Specialty malts of another sort - as needed. I brew 10 gallon batches, typically and a lot of Light German Lagers, so I can use up a sack in a month or two with regular weekly brewing. For hops, I buy German Magnum by the pound and Hallertauer, Mittelfrüh, Tettnanger, and East Kent Goulding’s by the half pound.
About once or twice a year when I brew at someone else’s house as a social get together with friends who homebrew, I may go to a kit (gasp!) to try out something new.
Edited to correct spelling.