Parama Ekadasi

Parama Ekadasi is recommended as nirjala or with water ideally.

As far as the "pancaratrika fast" is concerned Hari Bhakti-vilasa mentions three levels of fasting according to pancaratrika system.  I am giving them below:

Levels of fasting:

Devotees can choose whichever level of fasting as is convenient to them. It should not disturb their normal devotional service(s) and daily sadhana.

Level 1:
One can consume products of the cow (pancha-gavya) each for each day:
First day: Cow dung (Gomaya)
Second day: Cow urine (Go-muutra)
Third day: Cow milk (Kshiira)
Fourth day: Cow yoghurt (Dadhi)
Fifth day: All products of  the ccow mixed (Pancha-gavya)

Level 2 (this is what Jayapataka Swami followed for the last two years):
If one can't follow level 1, one can take fruits and roots

Level 3:
If one can't follow level 2, one can take "Havishya."

References: Padma Puraana, Brahma-khanda, Chapter 23; Skanda Puraana, Vishnu Khanda, Kaartika Maahaatmya section, Chapter 32; Garuda Puraana, Puurva Khanda, Chapter 123.

Ingredients for Havishya as mentioned in Sri Hari-bhakti-vilasa (13.10-13)
The following are ingredients that can be used in making Havishya, which is like a khichari made with these items.

* Aatap rice
* Ghee from cow
* 'Saindhava' salt (salt from ocean -  Sea Salt)
* Milk from cow
* Milk with cream
* Ripe banana
* Kaala-shaaka
* Wheat
* Fruits (Skanda Puraana, Naagara Khanda says they must be with a small seed or with few seeds only)
* Mango
* Jackfruit
* Labali fruit
* Roots except 'keaa' (a type of grass or root)
* Pippalii
* Haritakii
* Naagaranga
* Ikshu-dravya or sugarcane derivatives (other than gur or mollasses)
* No oil

The following ingredients are normally part of Havishya but have to be avoided in the month of Kaartika:

* Mung dal
* Til oil
* Beta-shaaka
* Shashtikaa-shaaka
* Radish
* Jeeraa
* Tamarind

Bhisma Panchaka
This kind of 5 day fast is also prescribed for the last 5 days of Kartika (Damodara) Month and it is known as "Bhisma Pancaka".  During that vrata puja offerings to the Lord are also prescribed.  I am listing them below. There are also mantras that go with these offerings.  However,  I didn't find any specific mention about this for Purusottama month.  In the Padma Purana it only stated that in addition to ekadasee one can observe a "pancaratrika" fast until amavasya.  Here are offerings prescribed for Bhisma Pancaka.

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Devotees may offer the following to the Deity form of the Lord:

On the first day, one must offer padma (lotus) flowers to the feet of the Lord
On the second day, one must offer bilva (wood-apple) leaves of the thigh of the Lord
On the third day, one must offer gandha (scents) to the navel of the Lord
On the fourth day, one must offer java flower to the shoulders of the Lord
On the fifth day, one must offer malati flower to the head (siro-desa) of the Lord

Reference: Garuda Puraana (op cit.)