Within Quip Documents, you can bold, italicize, underline, indent and strikethrough text, as well as choose from three different-sized headers or three types of lists (bullets, numbers or checklist).
We are continually working on adding additional formatting options. However, the formatting options in Quip will always be somewhat limited (re: you won't find 18 different bulleted list types or font sizes). This is a conscious design choice, as part of Quip's emphasis on simplicity and on enabling you to create documents that look beautiful and consistent on any device.
We're always happy to log and react to feedback (ex: do you really wish you had footnotes or superscript?) and you can always send feature requests via a Salesforce Case.