Several useful bag related APIs that you wish were built into the WoW API:

  local LBU = LibStub("LibBagUtils-1.0")
  
  for bag,slot in LBU:Iterate("BANK", "Major Healing Potion") do
    LBU:PutItem("BAGS")
  end

:Iterate("which"[, "lookingfor"])

which: string: "BAGS", "BANK", "BAGSBANK"
lookingfor: OPTIONAL: itemLink, itemName, itemString or itemId(number). Will not match partial names.

Returns an iterator that can be used in a for loop, e.g.:

for bag,slot,link in LBU:Iterate("BAGS") do   -- loop all slots
for bag,slot,link in LBU:Iterate("BAGSBANK", 29434) do  -- find all badges of justice

:Find("where", "lookingfor"[, notLocked])

where: string: "BAGS", "BANK", "BAGSBANK"
lookingfor: itemLink, itemName, itemString or itemId(number)
notLocked: OPTIONAL: if true, will NOT return locked slots

Returns:: bag,slot,link or nil' on failure

Finds the first instance of what you are looking for. To find all, use :Iterate() instead.

:FindSmallestStack("where", "lookingfor"[, notLocked])

where: string: "BAGS", "BANK", "BAGSBANK"
lookingfor: itemLink, itemName, itemString or itemId(number)
notLocked: OPTIONAL: if true, will NOT return locked slots

Returns:: bag,slot,size or nil' on failure

Finds the smallest stack of what you are looking for. To find all, use :Iterate() instead.

:PutItem("where"[, count[, dontClearOnFail]])

The easiest way to move items between bags and bank is of course to simply "click" them, but that doesn't work when you split stacks. That's when this function is handy.

PutItem is ''smart''; it will try to use specialty bags before standard bags. (But it will not try to put e.g. herb bags in herb bags. Doh.)

where: string: "BAGS", "BANK", "BAGSBANK"
count: OPTIONAL: number: if given, PutItem() will attempt to stack the item on top of another suitable stack. This is not possible without knowing the count, so if not given, it will simply be put in an empty slot. Default: nil.
dontClearOnFail: OPTIONAL: boolean: If the put operation fails due to no room, do NOT clear the cursor. Default: false. (Note that some other wow client errors WILL clear the cursor)

Returns:: bag,slot or false for out-of-room.; If called without an item in the cursor, 0,0 will be returned (slot 0 does not exist)

:LinkIsItem(fullLink, lookingfor)

fullLink: string: A full item link as given by WoW APIs
lookingfor: string: itemLink, itemName, itemString or itemId(number). Will not match partial names.

Returns true if "lookingfor" matches "fullLink". Ignores in-constant info (i.e. level / wobbly 3.2 randomstats) in links.

:MakeLinkComparator("lookingfor")

lookingfor: string: itemLink, itemName, itemString or itemId(number). Will not match partial names.

Returns a comparator function and two arguments, that can be used to rapidly compare several itemlinks to a set search pattern.

This comparator will

Ignore the 9th "level" parameter introduced in 3.0
Correctly match items with changing stats in inventory vs AH/Mail/GBank - see http://www.wowpedia.org/ItemString#3.2_wotlk_randomstat_items_changing_their_suffix_factors
Pick the smartest way to compare available

Example:

local comparator,arg1,arg2 = LBU:MakeLinkComparator(myItemString)
for _,itemLink in pairs(myItems) do
  if comparator(itemLink, arg1,arg2) then
    print(itemLink, "matches", myItemString)

:IterateBags("which", itemFamily)

which: string: "BAGS", "BANK", "BAGSBANK"
itemFamily: number: bitmasked itemFamily; will accept binary-OR:ed combinations of itemFamily values. 0 = iterate only regular bags.; nil: iterate ALL bags, including keyring and possible future "special" bags

Returns an iterator that can be used in a for loop, e.g.:

for bag in LBU:IterateBags("BAGS",0) do   -- loop all regular bags

:CountSlots("which", itemFamily)

which: string: "BAGS", "BANK", "BAGSBANK"
itemFamily: number: bitmasked itemFamily; will accept binary-OR:ed combinations of itemFamily values. 0 = iterate only regular bags.; nil: iterate ALL bags, including keyring and possible future "special" bags

Returns numFreeSlots, numTotalSlots. Note that the bank is considered to have 0 slots unless the bank frame is open.

:IsBank(bag)

Returns true if a bag is a bank bag (or the bag frame). Yes, easily coded yourself, but I did it right and used the FrameXML constants so it'll actually keep working when Blizzard adds yet another bag.

:GetContainerNumFreeSlots(bag)

Returns slots, family like you would expect. Except it actually works for the keyring also, which Blizzard's API does not.

:GetContainerFamily(bag)

Returns the bag's family. Including the correct bitmask for the keyring, which Blizzard's API does not.