MacGyvered chlorine gas protection
Interestingly, the British had such a solution in WWI: the Hypo Helmet. This was simply a bag soaked in sodium thiosulfate solution and worn over the head.  Thiosulfate reduces chlorine (and halogens generally) to chloride (halide) ions:

$\ce{2 S2O3^{2−} + Cl2 → S4O6^{2−} + 2 Cl^{−}}$

As the article notes, this was not the best solution, but I think it fits your criteria for rough and ready protection.