This is an interesting question. I think quite a bit about this too, because most of my life's savings is set aside in a "gone to hell" fund (for use only if everything else has, well, I won't write that twice). There is no safety like cash safety for immediate liquid purposes, but suspending disbelief on 2008-like scenarios, there are some exchange tradable instruments that can be risk-weighted with other dividend paying exchange-traded instruments. The goal here is simply to beat US money markets. The sitting period for some of these is 1 month to 2 years, unless you need a dump truck to hold the amount, in ascending order of risk;

LQD paired with either TLT, IEF, or both. Both UST funds yield comparable to their govvy bases and weigh out the relatively small risk in the AAA corporates. All pay monthly, which is nicer than quarterly.

An exchange traded income fund (PMX, PFN) paired with TLT, IEF, or both. Same as above, also paid monthly, has the advantage of smaller entry prices.

A dividend aristocrat like EMR, paired with TLT, IEF, or both. Share volatility risk, of course, so this would have to be risk weighted.

A HY flier MLP like LINE or BBEP paired with TIP + UUP. Risk weighting would be for inflation/deflation risk. The TIP has been on a bit of a tear lately, and the UUP pays no divvy, so the quantity of UUP would represent your outlook for deflation.

One that I used myself last year was cyclical - under $48.50 I believed the FLAT (UST 2s10s flattener ETF) was a steal, and it was. Right now its inverse STPP is also a steal if held over the next 8 months - 1 year. I think it's good for 15-20%. The only drawback with these two lovely instruments is their relative illiquidity. STPP is lucky to trade 2000 shares a day. Still, if you believe that it is impossible for the 2s10s to remain historically supine for another year, then buying up the offer book a couple times a week is still a good bet - when the 10y hits 3.5% again with the 2y stuck at .65, the liquidity will be there.