If you have an sheathed weapon in a Handy Haversack that you have within reach (IE tied to your belt), can you both reach for said weapon and unsheath it in a single action? Or does drawing a weapon from a Handy Haversack and drawing it from its sheath count as two actions?
Some weapons have to be sheated before being put into a handy haversack or they risk perforating it. You still need to unsheat them after drawing them, unless you have the Quick Draw feat or the Magic Item Compendium weapon crystal that doubles the feat.
Using a club or some other weapon that does not need to be sheated could be a nice alternative.
To retrieve a weapon from a haversack then draw the weapon,
Usually This Takes 2 Move Actions
Heward's handy haversack (DMG 258) (2,500 gp; 5 lbs.) says
A backpack of this sort appears to be well made, well used, and quite ordinary. It is constructed of finely tanned leather, and the straps have brass hardware and buckles. It has two side pouches, each of which appears large enough to hold about a quart of material. In fact, each is like a bag of holding and can actually hold material of as much as 2 cubic feet in volume or 20 pounds in weight. The large central portion of the pack can contain up to 8 cubic feet or 80 pounds of material. Even when so filled, the backpack always weighs only 5 pounds.
While such storage is useful enough, the pack has an even greater power in addition. When the wearer reaches into it for a specific item, that item is always on top. Thus, no digging around and fumbling is ever necessary to find what a haversack contains. Retrieving any specific item from a haversack is a move action, but it does not provoke the attacks of opportunity that retrieving a stored item usually does.
Emphasis mine. So even if a creature's strapped the magical backpack to his belt (somehow), it's still a move action to retrieve the weapon from the haversack as removing any item from it is a move action.
Then Things Get Slighty Murky
I'd argue, after retrieving the weapon from the haversack, then the weapon must be drawn, and that there is no distinction between unsheathing a weapon and drawing a weapon--the term drawing a weapon is an abstraction used to indicate what one does to ready one's weapon usable in combat. The Player's Handbook makes this fairly clear:
Draw or Sheathe a Weapon
Drawing a weapon so that you can use it in combat, or putting it away so that you have a free hand, requires a move action. This action also applies to weapon-like objects carried in easy reach, such as wands. If your weapon or weapon-like object is stored in a pack or otherwise out of easy reach, treat this action as retrieving a stored item.
If you have a base attack bonus of +1 or higher, you may draw a weapon as a free action combined with a regular move. If you have the Two-Weapon Fighting feat (page 102), you can draw two light or one-handed weapons in the time it would normally take you to draw one. (PH 142)
Thus, once a weapon's been retrieved from the haversack, it's within "easy reach," and can be drawn like any other weapon within easy reach, usually by taking a move action or drawn simultaneously when the creature takes a move action to move up to the creature's Speed. The draw a weapon action must occur even if the weapon's a spear, mace, or sword. Maybe the haversack always spits out the spear at an awkward angle or whatever.
A more simulationist reading of the above allows a weapon that is never put in a kind of container to be used immediately, without the need to draw it. For example, the simulationist would argue, retrieving a spear from a haversack should be sufficient to let the spearman attack with it immediately without the need to draw it further.
The problem is that when the Player's Handbook says that a weapon's "cost includes miscellaneous gear that goes with the weapon, such as a scabbard for a sword or a quiver for arrows" (PH 114), it doesn't go on to detail which weapons include miscellaneous gear such as an appropriate container, leaving such judgment entirely up to the DM. Should a spear be stored with a leather wrap covering the tip? Probably. But only the DM knows for sure, and only the DM knows if he wants that kind of detail to matter.
Further, while the bag of holding (DMG 248) (2,500+ gp; 15+ lbs.) says that
If the bag [of holding] is overloaded, or if sharp objects pierce it (from inside or outside), the bag ruptures and is ruined.
the haversack doesn't say this. However, the DM could rule that because each pouch is like a bag of holding, the bag's rupture-and-ruin clause applies.