[Phanx]

You have a scoping problem.

for k, v in pairs(flasks) do
	local flask =  UnitBuff("player", k)
	-- "flask" is local to this scope.
end

-- "flask" does not exist in this scope.
if (not isGuildGroup and food) or (isGuildGroup and flask and food) then
	ReadyCheckFrame:Hide()
	ConfirmReadyCheck(1)
end

Also, you may want to change your GetSpellName function to return an empty string, or UNKNOWN, or some other "dummy" value for spell IDs that don't return a real name. Otherwise, if Blizzard changes a spell ID, you will end up with holes in your otherwise sequentially-indexed table.

Also also, since you are using an indexed table, you should use for i = 1, #flasks do local k = flasks[ i ] instead of for k, v in pairs(flasks) to avoid the slow call to pairs.