A holy dip in the river Ganges is what most people come to the Kumbh for - but Ganga Pooja - a ritual worship of the river is as much important according to the local Pundas (priests). A Pooja is a ritual where offerings are made to Gods according to ancient religious rituals, each made along with the chanting of mantras (sacred verses). The Pundas who will help you carry this out can be found along all the major Ghats (banks) by the Sangam.

But before visiting your Punda, you need your Pooja Kit - offerings to be made to the Goddess Ganga. As with the general run of offerings in Hindu rituals, almost all the needed materials are chosen as tokens, symbols, of nature’s bounty - flowers, fruit, milk and so forth. We consulted Gopal Das Panda and prepared a list of things you need to buy for your Pooja.
Coconut:

The coconut is always considered an auspicious offering for the Hindu Gods. The coconut should be one with water inside and husk outside. Though coconuts are usually broken before they are offered to most Gods, remember that Mother Ganga likes them the way they come naturally.

Price: Rupees ten.
Garland:

A Garland of flowers - traditionally Genda (marigold) is used in this region. No Hindu ritual is complete without at least a token flower.

Price: Rupees ten.
Milk:

preferably from a cow, not a buffalo or goat. Milk has a long association with purity in Hindu belief and the cow has its own, revered, place.

You can pay any amount you want.
Incense:

generally a bunch of sticks of these.

Price: Rupees two
Camphor:

This is to burn for the arati, the waving around of a complete circle of flame, another ritual essential in a prayer. Fire is a fundamental in any Hindu propitiation of a deity.

Price: Rupee One
Raksha:

The term for a thin bunch of cotton threads, worn around the wrist after a symbolic offering to the Goddess, as a good-luck talisman.

Price: Rupees two
Chunri:

A head-covering for women in much of the rural north here, included as an offering to the Goddess.

Price: Rupees ten
Sindur:

A pinch of sindur - an auspicious sign for married women and for markings.

Price: Rupee one
Daan:

Gifts, to the priest, to be offered from any of 84 possible items, including money, clothes, gold, etc.
All these items are available along the Ghats at the price mentioned above, though all retailers are open to negotiation.