I need to keep creamed peas and potatoes warm all day.

All day? That's a long time for something that will reduce down to nothing. You're better off chilling them and re-heating. If you are putting them in a lunch or traveling, try pre-heating a thermal container -by putting boiling water in it for 10-15 minutes then draining it (one of those Thermos soup containers). They won't reduce down in the thermal container, but they won't be fresh and bright like peas should be either.

If it's a situation where people will be in and out all day, so you literally need it warm "all day," try setting the pot over a pot of simmering water (just be sure to check the level and re-fill as needed so your bottom pot doesn't burn at some point).

Another option is a slow cooker (aka Crock Pot), set to low and covered. Will still reduce down some, but you can add back water and stir from time to time as condensed water drips back in from lid.

I would suggest making a big batch of the food then keep some warm and put the rest in the fridge, then heat up a little at a time as needed. The food will be fresh that way.

Similar to Barnaby, I say use a slow cooker but set it to Warm. Most slow cookers have the Warm setting, and that will not be hot enough to cook anything, but will keep it at a warm temperature. Just remember to stir occasionally to keep it evenly warmed, and to keep a skin from forming on the cream sauce.