General lack of fancy:
* Plain
* Simple
* Unpretentious
* Basic
* Modest
* Down-to-earth
* Humble
Informal or casual:
* Informal
* Casual
* Relaxed
* Everyday
* Practical
Lacking elegance or sophistication:
* Rough
* Crude
* Unrefined
* Unpolished
* Gauche
Lacking luxury or extravagance:
* Inexpensive
* Affordable
* Frugal
* Budget-friendly
* No-frills
Other words depending on the context:
* Rustic (for something simple and made from natural materials)
* Functional (for something that is practical and useful)
* No-nonsense (for something straightforward and direct)
The best word to use will depend on the specific situation and what you want to communicate.