I use Oasis Max-Life florist foam for all my wedding and other fresh designs. I've seen "comparisons" made by online crafters - some who claim that cheaper foam works better than Oasis.
I have my doubts. I've worked in flower shops since the late 1990's and have had opportunity to experiment with many different brands of products. I kept coming back to Oasis because it's the one I had the most consistent success with.
I don't get paid to give this kind of review - it's what I sell because it's WHAT I USE.
I do want to offer a word of caution . . . I often see florist foams offered at deep discounts both at dollar stores and online auctions. Take care - because any foam can degrade with time and not work as well in absorption. Some sellers like these are selling buyouts or discontinued merchandise. They may (or may not) be able to stand behind the quality of their product.
Buying from a well known florist supplier who sells to local and national flower shops ensures frequent turnover of common products (including foam). That way you are assured that you will receive a foam product while they are still at high quality and absorb water well.
I usually recommend soaking your Oasis in water treated with a flower food. Disregard that, however, when you are creating Christmas arrangements. Christmas greens have a long life and you'll probably be replacing the flowers while the greens will still look good (as long as they are kept well watered.)
Flower food can cause some greens to turn yellow early, thus I don't tend to soak my Oasis in it.
Do, however, cut and process your fresh flowers correctly and let them rest in a bucket that has been treated with flower food.
This way both your greens and your fresh flowers have optimum chance of having a long life.
Always allow florist foam to "float soak" - sinking gradually to the bottom of the container as the foam takes up water. A single Oasis brick can hold up to 2 quarts of water!
Forcing the brick underwater can cause dry pockets in the foam, which could spell early death to any flower stem that rests inside that pocket.
Good quality foam takes only a few minutes to thoroughly soak and take up sufficient water.
Cut off the amount of foam that you'll need to fill your novelty container. You will have to trim and shape the foam to fit into the shape of the opening of your own container.