Regarding IRAs. If you plan a sabbatical around a tax year (and are not making any earned income during that year), I don’t think you can technically contribute to an IRA. Only earned income can go into an IRA. In reality, this will only be an issue if you get audited, but probably good to know upfront. Second, why not just contribute to a Roth IRA via the backdoor during working years assuming you make enough that you can’t contribute directly?

With regards to chasing yield for short term savings, I think money market funds are a great option. More liquidity than CDs or bonds. If you are in a higher tax bracket, you can invest in a municipal money market fund which is federal tax exempt, and then easily switch money into a more traditional MMF during periods where your tax bracket is lower. You have to run a quick calculation comparing municipal MMF vs non-municipal MMF vs high yield savings account to see which one is giving highest real yields at any given time based on current rates and your current tax situation, but this is easily done and get help maximize cash investing while essentially maintaining the liquidity of cash.