Many of the days of the week are named after ancient nature gods, many of which trace to PIE:

PIE sóh₂wl̥ (“sun”) → Proto-Germanic sunnǭ (“sun”) → Old English sunne (“sun”) → Old English Sunnandæg (“Sun's day”) → Middle English Sonday / Sunday → Sunday

PIE mḗh₁n̥s (“moon; month”) → Proto-Germanic mēnô (“moon”) → Old English mōna (“moon”) → Old English Mōnandæg (“Moon's day”) → Middle English Monenday / Monday → Monday

PIE deywós → Sanskrit deva, “god” → Latin deus, “god” → Old Norse Týr, the god → Old English Tīw → Tīwesdæg (“Tiw's day”) → Tuesday

PIE dyew- (“bright sky; daylight”) → deywós (“celestial one; god”) → Proto-Germanic Tīwaz → Old English Tīw → Tīwesdæg → Tuesday

The reconstruction exists for the remaining days too, but is more uncertain when tracing it to PIE:

PIE weh₂t- / related roots concerning excitement or inspiration → Proto-Germanic *Wōðanaz → Old English Wōden → Wōdnesdæg (“Woden's day”) → Wednesday

PIE (s)tenh₂- (“thunder”) (reconstruction/derivation has some uncertainty) → Proto-Germanic þunraz (“thunder”; the god Thunder/Thor) → Old English Þunor → Þunresdæg (“Þunor's day”) → Thursday

PIE prih₁- / preyH- (“to love; be dear”) → Proto-Germanic Frijjō (the goddess Frigg, approximately “beloved/dear one”) → Old English Frīg → Old English Frīgedæg (“Frīg's day”) → Middle English Fridai / Friday → Friday

Saturday is not known to trace to PIE:

Latin Saturnus → Old English Sætern(es)dæg (“Saturn's day”) → Saturday