Hi Adam ,
Some believe that the last common ancestor of Homo and Pan was an animal close to our modern day chimp and the type of tools I envisage being used by the first of our obligate bipedal ancestors would be similar to those used by modern day chimps or monkeys . Such tools would include large sicks , rock and anvil assemblages (Capuchin monkeys ) or simple ,hand held throwing items . The main point to remember is that an early biped could likely develop more power in the tools making them more effective . It's not so much that a chimpanzee like animal can't figure out that a long stick could be a good weapon ,it's just that they lack the phenotype to make using such a weapon worthwhile . (see 2 min video below it shows two chimps in conflict . One tries to use a long stick as a weapon on it's opponent but soon drops the stick when this approach fails . The first 50 secs of the video can be skipped )

The modern gibbon probably lacks the marbles to swing or throw a stick to great effect but if you combine a chimp brain with a gibbon like phenotype you are in business with a high speed tool user . This , I believe , is probably why our earliest bipedal ancestors remained bipedal when they gave up a brachiating lifestyle .

So here is that video . The stick wielding chimp seems to try out the stick as a weapon with a few practice swing before going after its troop mate . This fails .
Now imagine the damage a five year old child could cause swinging a golf club at a car door . Our early ancestors would not have golf clubs but may well have had a access to heavy woods such as ironwood . So for early bipeds its not about more sophisticated tools but about the more sophisticated use of tools which is allowed by a bipedal phenotype .

Crazy Chimps Fighting at the LA Zoo (with a big stick)! - YouTube

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3 Jan 2012 - Uploaded by dancheng2
Crazy chimps beat each other, chase one into a ravine, and in the finale, a chimpuses a big stick to beat ...