I've been doing some local training hikes during rainy conditions, some days raining when I start, some rain starts later. I am reminded by nature, once again I might add, that it is best to put on rain pants before it starts to rain. With no shelter, it gets a little tricky getting stuff out of the pack and still keeping the pack and contents dry.
In my case, I have a Packa which is a rain poncho with sleeves or a rain jacket with a hump for the pack, whichever you want to call it. It keeps the pack quite dry, but to get in the pack I've got to take it off and expose myself to the elements. For now I have a Patagonia Guide Jacket which is water resistant and a warm layer in the outer mesh pocket, and I grab that during brief stops to get something from the pack.
If it is raining at the start of the hike, and expected to continue all day, I will start with rain pants on, and also wearing my Seal Skinz socks and my trail runners, and will be fine all day. If the terrain is not steep, I will also have an umbrella. If I am out on the trail and the rain starts I will just accept the wet legs and feet if is our normal weather. I generate enough heat hiking to stay warm during our normal wet weather. If it is a cold storm I will go ahead and put on the rain pants over my wet synthetic pants, just for the added warmth. So far I have not put on Seal Skinz once my feet get wet.
Yesterday I went a little further than planned, ending up with 18+ miles, and realized another thing about pack covers and wet weather. On a real trip, I will use a bladder, but on these training hikes I just stick a water bottle in the side pocket of the pack. It is a real pain to get that water bottle out without taking off the pack, so it is easy to get somewhat dehydrated. My advice: If you are using a pack cover, use a water bladder.