Starting a hike hampered by leg injury is a novel scenario.

If the forecast was for warm weather and the area in which you were hiking is not remote and especially prone to sudden weather changes (i.e. big mountains), then I'd go ultra-light, on one condition:

1) at least two friends/family not on the hike were aware of my precise route (hiking and driving) and prepared to alert police/rangers if I did not report in by a certain time.


For such a day hike in warm weather (day and night) with a reasonably reliable forecast and friends on alert (I would not hike alone, ever), I would go ultra-light:

Hiking poles
water (+ micropur tablets)
2 energy bars
first aid (pain reliever, band-aids)
Survival blanket-tarp (AMK heatsheet or some such)
large garbage bag (for use as emergency poncho)
small amount of paracord
Fire tools: Bic lighter, matches, firesteel, cotton balls + petroleum jelly
Knife
titanium or stainless cup
Esbit titanium stove + fuel tablets
compass w/mirror
Fox 40 whistle
Petzl Zipka head/wrist lamp
pen and paper (serves as fire tender as well as for writing notes-vital info)
duct tape (now wrapped around my Bic lighter)


With such potential to further the injury and be rendered lame, I would seriously consider putting my very light Marmot Dri-Clime jacket (lightly fleece-lined and highly water resistant) in the bottom of my pack.