Summarizing the remaining 'toolkit' available for dealing with a recession or financial crisis -
1) Interest Rates - (status - limited) - US has 2% available to get to ZIRP, then would have to go into NIRP. Europe, Japan are already near ZIRP or in NIRP.
2) QE - (status - limited) - Fed balance sheet is currently $4 tril, they could go to 6 tril, with upper limit at 8, 10, or ?
3) Deficit Spending - (status - limited) - current annual budget deficit is already $1 tril or more
4) Tax Cuts - (status - limited) - was already done last year
5) Helicopter Money - a variation on #3, where money is handed out to the population directly
6) Dollar Devaluation - to boost exports, but other countries quickly follow suit, so any benefit is fleeting (currency war)
7) Tariffs - other countries quickly retaliate, global trade is reduced (trade war)
8) Devalue dollar vrs gold - (1933)
9) Shooting War
10) SDR/Special Drawing Rights (IMF bailout of the world) - all roads ultimately lead here