I have 4 guild banks of my own and it's hard to keep track of a max capacity character bank for each, plus my main, plus 6 bank tabs (4 gbanks, +1 tab on two)... I'm really bad about not selling stuff, you never know when you'll need it
. Either Combuctor or Carbonite tells me how much stuff I have on mouseover (probably other options also, between the two). I pretty much just know where everything is without them, though, because some stuff I've kept since vanilla (before guild banks
).
I've been meaning to try Altoholic, but so far I only use alts for storage... Combuctor and/or Carbonite have done fine for this, for me.
/agree with Seerah about mail, the time limit has eaten much from me, due to my old age.