The basic choice on the radial situation is one of elevated radials vs. radials on the ground. If you choose elevated radials, then cutting 2 minimum for each band would be the way to go. This can obviously get out of hand if more than 2-3 bands are involved.
With radials on the ground, you will typically want a certain number that are all equal length. In this scenario, you are trying to make the ground behave as a conducting surface. The best overall length depends up how many radials you can lay down. See –
If you only want to do one band, I’d suggest 3-4 elevated radials cut to the right length(1/4 WL) for the band you are on.
If you want a multiband setup, I’d go with perhaps 4-8 radials on the ground cut to 1/4 wavelength or less for the lowest band that you want to operate on. Note that the table in the link above suggests shorter ground radials for low numbers. My experience is that this is good advice if you are in the range of 8-32 radials. Setups with small numbers of ground radials might need longer ones to get the antenna to tune up properly (but never more than 1/4 WL unless you have more than 90).
Given your goal to setup portable on multiple bands, I think I’d recommend the second scenario (4-8 ground radials) as the practical one for you. If you also plan to setup your antenna at your Home QTH, you could either do either elevated radials or radials on the ground with say 16-32 buried radials centered at the location where you plan to setup your antenna for operation from your home qth.
There are obviously lots of choices between these two. Also, performance for any such installation will depend upon the conductivity of the ground at the actual site where the antenna is installed.
Note that in Patrick’s situation, his radial system is essentially an elevated one and radials of 1/4 WL are needed.