peppers have an extensive root system,
for a smaller sized container, I'd stick only
one
plant..
You might be able to grow different lettuce's under them,
as they are shallow rooting and wouldn't interfer with the deeper roots of the
pepper plants..
Also Tomato
plants can *and should have a deep planting
to establish good roots for the support of the taller
plants,
and also lettuce can be grown there..
And lettuce appreciates' some shade
provided by those
plants, in the hot summer time...
You can have blocks of corn with either
beans or peas grown up the stalks...
*just make sure you give the corn a good head start to establish, before putting in the beans/peas..*
and the beans and peas will put nitrogen back into the soil for the heavy nitrogen feeding corn loves..
*make sure soil in your bucket is filled with good soil, compost and vermiculite/perlite to give it light, airy texture and provide good air/oxygen for the roots of the
plants...*
Here's a bucket I have just for some peas,
but you could put in 6 corn in an outter circle and then the beans/peas up the stalks at each base..