The only urban environment I found a need for a bigger fixed blade was Baghdad.

As for the PPK, I would rather have it in my knapsack than in an unattended car. Without a jacket, I reckon it'd be hard to conceal any decent firearm without it printing or otherwise becoming visible at some point. If you had a desk I'd say keep it locked up in there, but that also invokes a certain amount of exposure during the transition. If you can't keep the knapsack under regular scrutiny, then perhaps the car is the only option, but I would keep it well secured in a lock box or some such then.